We're down to the final eight teams vying for UEFA Champions League glory; can Liverpool get revenge on Real Madrid for defeating them in the 2018 final? How will Bayern Munich and Paris Saint-Germain fare in a rematch of last year's decider? Are Man City facing an easy road, or will Erling Haaland and Dortmund take them down? And how about FC Porto? They may be considered "minnows," but they had enough talent to stun Cristiano Ronaldo and Juventus; are Chelsea next?

ESPN breaks down everything you need to know ahead of this week's first legs, including where the games will be won or lost and key players, as well as predictions as to who will go through.

Jump to: Real Madrid vs. Liverpool | Man City vs. Dortmund | Bayern vs. PSG | FC Porto vs. Chelsea

Tuesday

Real Madrid vs. Liverpool
3 p.m. ET / 7 p.m. GMT

Overview: "Revenge, redemption and Ramos" is how you can subtitle this clash of Euro Titans, who have lifted the trophy a combined 19 times and are well acquainted (from six matches, there have been three wins apiece, two finals split evenly and, when they have fought recently, oodles of goals.)

Revenge? Well that's uniquely for Liverpool. Last time the sides met was the 2018 Champions League final in Kiev and Jurgen Klopp's Reds saw red. Mohamed Salah was carted off injured after being run over by Sergio Ramos, then concussed goalkeeper Lorius Karius gifted Madrid two goals to hand Zinedine Zidane his third-straight UCL title.

Revenge, no matter how often it is denied as a concept, is a spur, and both teams' seasons need redemption. Madrid are still in contention for La Liga but their title defence has been pock-marked by ugly, unpredictable defeats. Liverpool always desire this trophy but, sitting sixth in the Premier League as this tie kicks off, they now require it.

And Madrid captain Ramos. Injured, again. Not present to torment Liverpool, or to inspire his own club. Out of contract in June, not certain to stay. Might this tie, if Madrid are eliminated, prematurely end his love affair with the Champions League?

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Where Real Madrid will win or lose: Their name has been etched on this trophy four times in the last six years, but along the way, not just this season against Inter and Borussia Monchengladbach, there have been near disasters, impossible rescues and football-escapology of the grandest kind. Remember Dortmund and Atletico in 2014? Wolfsburg and Atletico (again) two years later? Bayern Munich in 2017 or Juventus 12 months after that? Examples all of brinksmanship extraordinaire.

Madrid are addicted to conquering Europe and, should they knock Liverpool out, this vitamin of absolute dedication to lifting the trophy will undoubtedly have nourished them. But, in playing terms, they won't win this tie unless three compartments of their magic box are working fluidly: Striker Karim Benzema, goalkeeper Thibaut Courtois and that immense midfield of Luka Modric-Casemiro-Toni Kroos. In other words: "Score, save and scintillate."

Where Liverpool will win or lose: Liverpool slightly resemble Barcelona, in that injuries have forced them to look inward to solve problems they didn't have a clue they were going to suffer. Just as the Catalans have been elevated from the mire by youngsters like Pedri, Ronald Araujo, Oscar Mingueza and Ilaix Moriba, Klopp has found in-house sustenance from competition debutants Nat Phillips, Rhys Williams, Curtis Jones, Neco Williams and Caoimhin Kelleher. Average age 20, but 18 Champions League appearances between them this season.

Throw in Kostas Tsimikas and 21-year-old Ozan Kabak sharing the load in their first season at Anfield and you'd be forgiven for branding this "all change." But the same old elements of flying wing-backs, hostile pressing, lightning counter-attacks and the Sadio Mane-Roberto Firmino-Mo Salah trident remain Liverpool's DNA.

Key players: There will, in such an historic tie, inevitably be a jack-in-the-box player who excels like Divock Origi or Gini Wijnaldum (who popped up for Liverpool against Barca in 2019), or how substitute Gareth Bale and Ferland Mendy did for Madrid in, respectively, that 2018 final and the last-16 first leg against Atalanta this season.

But the principal threats favour Liverpool. First, when they muster up that hurricane-football that has trademarked Klopp's reign, it is precisely what this slightly-ageing, one-paced Madrid hate. Second, Liverpool's principal strength is devastating forward play and combinations, which directly threaten a Madrid backline missing gnarled warriors in Ramos and Dani Carvajal. That Klopp incorporated the prolific, and now fully fit, Diogo Jota alongside the star trio in a 4-2-3-1 formation whilst destroying Arsenal 3-0 at the weekend is ominous.

Nor is Zidane averse to tactical tinkering. Frankly, his experiments with 3-5-2 look ill advised, but if he does employ that system against Liverpool it will require Marcelo (still ultra-talented and eccentric, but in decline) to absolutely excel and to make better positional judgements than normal. The key five for Spain's champions are Courtois, who has been at or near his very best form this term; Modric, Casemiro, Kroos, who can take a game away from the best opponents because, technical skills aside, they live and breathe the winning mentality; and Benzema, who not only has 11 goals in his last 10 matches, but the effervescence of his play, his invention, vision and technical skills are sheer magic to watch. On form he can win this tie. Madrid, were they to lose him, would be lost.

Prediction: Like Rafa Benitez said this week: "I don't see a clear favourite." Madrid can win and it is to their advantage they won't face the coliseum atmosphere of a full, rabidly loyal Anfield. However, Liverpool look like they are coming back to form. They can count on more of their proven winners back in the squad, are spurred by the revenge instinct and are marginal favourites if they can press Madrid out of their preferred tempo. -- Graham Hunter

Man City vs. Borussia Dortmund
3 p.m. ET / 7 p.m. GMT

Overview: Recent form suggests this quarterfinal will be something of a mismatch, with City on course for a quadruple after winning 26 of their last 27 games in all competitions and Dortmund slipping seven points adrift of the Bundesliga top four following Saturday's 2-1 defeat to Eintracht Frankfurt -- their fifth loss in 11 games. But while City are overwhelming favourites, Pep Guardiola's team have repeatedly been beaten by unfancied opponents in the Champions League knockout stages, with Monaco, Tottenham and Lyon eliminating them in recent years.

In Erling Haaland, this season's leading scorer (10 goals) in the Champions League, Dortmund possess a striker capable of hurting City and triggering a repeat of their previous shock exits, but the likely absence through injury of Jadon Sancho, a former City youngster, will blunt the German team's cutting edge.

Where Man City will win or lose: While the focus on City often falls on their attacking capabilities, their run to the quarterfinals this season has been built on their solid foundations at the back, with Guardiola's team conceding just one goal in eight games. Ruben Dias and John Stones have formed an impressive central defensive partnership, although Aymeric Laporte has recently been paired with Dias, so Guardiola has options to contain Haaland.

As a team chasing a quadruple, City's weaknesses are in short supply, but they do lack a centre-forward capable of deciding a tight game. Sergio Aguero, who will leave when his contact expires this summer, is still short of fitness after injuries and period recovering from COVID-19, while Gabriel Jesus is not elite quality. But goals from wide and midfield have made up for that shortcoming this season.

Where Dortmund will win or lose: Dortmund's big strength is Haaland, the 20-year-old who has taken the Champions League by storm since scoring a debut hat trick for FC Salzburg in September 2019. Since moving to Germany the following January, the Norwegian striker has continued to score at an incredible rate of consistency. His pace and strength, allied with a nerveless approach to finishing, have made him the most sought-after player in world football.

Yet Dortmund have conceded nine goals in the competition this season at an average of 1.13 goals per game, so are likely to have to score at least twice to beat City. Moreover, one big advantage that Dortmund can usually rely upon in the Champions League -- a full and noisy Signal Iduna Park -- will be denied them this season because of the restriction on supporters due to the pandemic.

Key players: The strength of City is borne out by the fact that they don't have a single "key" player. While Kevin De Bruyne, Raheem Sterling, Ilkay Gundogan and Phil Foden have match-winning qualities, the team has carried on regardless. Guardiola can rotate his players without worrying about the absence of one pivotal player; even goalkeeper Ederson has been replaced by American Zack Steffen without consequence.

It is a different story for Dortmund, where everything revolves around Haaland, especially with Sancho expected to miss both games. That said, if City allow midfielders Marco Reus, Jude Bellingham, Julian Brandt and Thomas Delaney to get a grip of the game, it could make for a difficult tie for Guardiola's side.

Prediction: Man City to advance. Dortmund have the players to win over 90 minutes, but in a two-leg tie, it is impossible to envisage Guardiola's team not defeating the Germans to claim a place in the Champions League semis for only the second time. -- Mark Ogden

Wednesday

Bayern Munich vs. Paris Saint-Germain
3 p.m. ET / 7 p.m. GMT

Overview: A rematch of the 2020 Champions League final, which Bayern won 1-0, was prefaced by both teams playing vital league game at the weekend. While Bayern won 1-0 at RB Leipzig to stretch their cushion at the top of the Bundesliga to seven points, PSG lost at home to Lille by the same scoreline.

The Bavarians won their game thanks to a Leon Goretzka goal and another great performance from goalkeeper Manuel Neuer; PSG boss Mauricio Pochettino, meanwhile, was outsmarted tactically by Lille counterpart Christophe Galtier and Neymar, in his first league start in two months, was sent off late on after a disappointing display. Bayern striker Robert Lewandowski and PSG midfielder Marco Verratti will be crucial absentees in this tie, but only one team has shown it can cope without a star man.

Where Bayern will win or lose: Even without Lewandowski (and his 42 goals in 36 games in all competitions this season), Bayern are sure of their strengths and have self-belief that they can beat anyone. Goretzka and Joshua Kimmich form the best midfield duo in the world and unless PSG can stop them dictating the game, Bayern will come out on top. To replace Lewandowsi, manager Hansi Flick played former PSG striker Eric-Maxim Choupo Moting against Leipzig, while he also has the option of using Serge Gnabry or Thomas Muller.

However, despite Neuer's brilliance, this Bayern team concedes chances and goals -- 35 already in this season's Bundesliga -- and their high defensive line could be an issue against PSG's quick attacks.

Where PSG will win or lose: PSG must play with intensity and discipline, and be efficient in the press and counterpress. Kylian Mbappe will also have to be the star and exploit Bayern's high line. If he shines like he did when scoring a hat trick against Barcelona in the previous round, the French champions have a chance.

Yet PSG have also looked vulnerable in defensive transition during big games. Pochettino will have to replace Verratti -- a huge loss as no-one in the team has his creative touch -- while Neymar, while a certainty to play because he is so talented and can win the game with one moment of brilliance, is not 100% fit and struggles to be decisive in such situations.

Key players: Collectively there is no team better than Bayern, but Kimmich is the leader. The Germany international dictates the pace of the game, attacks, defends, recovers the ball and keeps things moving forward. In goal, the 35-year-old Neuer is looking at his best, while Muller is one of the most intelligent forwards in the game. Former PSG winger Kingsley Coman, who scored the winner in last year's final, will be motivated to break his old team's hearts again.

For PSG, Mbappe holds the key. On a good day he is unstoppable, as he showed against Barcelona, and he wants to make amends for the chance he missed against Bayern in 2020's final when the score was 0-0. Keylor Navas has also been fantastic in goal and has saved PSG many times while, without COVID-stricken Verratti, Neymar and Angel Di Maria will be the two main sources of creativity.

Prediction: Bayern will go through. Losing a player like Lewandowski is a huge setback, but PSG are losing as much, if not more, with Verratti out. Bayern are a machine; under Pochettino, PSG have only just started to assemble their engine. -- Julien Laurens

Porto vs. Chelsea
3 p.m. ET / 7 p.m. GMT

Overview: Porto are underdogs, but underestimate Sergio Conceicao's side at your peril. Their last-16, away goals, win over Juventus was remarkable; playing for an hour with just 10 men in the second leg and turning in a performance of defensive stability and ruthlessness in front of goal to knock out Andrea Pirlo's side. On the domestic front, they are unbeaten in the Primeira Liga since October, but only second in the table, some way off leaders Sporting.

Chelsea looked settled and resilient under Thomas Tuchel, until they came up against relegation-threatened West Brom, who stormed Stamford Bridge to win 5-2 after Thiago Silva was sent off in the 29th minute. It was a remarkable capitulation, given Chelsea were unbeaten since Tuchel took over in January and had conceded just two goals. But they will hope that was a mere freak result, rather than their bubble bursting.

Due to COVID-19 quarantine and travel restrictions, both legs of this quarterfinal clash will take place on neutral ground in Seville.

Where Porto will win or lose: Judging by their two legs against Juventus, Porto are accustomed to being underdogs and happy to stack their defence -- sometimes operating with six at the back in the previous round -- then focus on counter-attacking. They will be without Mehdi Taremi and Sergio Oliveira through suspension for the first leg, which will make a firm dent in their attacking power, but will look to squeeze the middle of the field, rather than pressure high up the pitch.

Chelsea will be given license to play out from the back, with Porto looking to tempt them into moving numbers forward. Porto's right flank is excellent, with Jesus Corona a threat, but with Taremi suspended, they may go with just one attacker, Moussa Marega, up front. Veteran defender Pepe missed out their weekend game through injury, but is optimistic he will be fit to face Chelsea.

Where Chelsea will win or lose: Chelsea will look to boss proceedings in the same way they did against Atletico in the Round of 16 and can expect to have plenty of the ball -- Porto had just 34% and 31% possession against Juventus in their two legs -- but need to make that count. Timo Werner is still finding his feet with just five goals in 29 league matches, but there is enough class in the likes of Hakim Ziyech, Kai Havertz and Mason Mount to provide the goals.

Porto will take notice of how vulnerable Chelsea looked defending crosses against West Brom, as well how susceptible they were to counter-attacks. Chelsea look set to be without N'Golo Kante and Christian Pulisic on Wednesday through injury, but expect them to line up in their usual fluid system of three centre-backs, two wing-backs, two sitting midfielders and three attackers.

Key players: Pepe, 38, is Porto's main man at the back and was sensational against Juventus. That they managed to prevent Cristiano Ronaldo from scoring in either leg is testament to their defensive stability, but they must be ruthless in front of goal. Corona is an outstanding threat, while Chelsea will also be mindful of Malang Sarr, who is on loan from the London club. And keep an eye out for left winger Luis Diaz, attacking midfielder Otavio and ex-West Ham striker Toni Martinez.

Mount is Chelsea's main man, but Tuchel will have to juggle the rest of his attack. It will be fascinating to see whether he opts with Werner as the sole No. 9 or, like he did in the first leg against Atletico, picks Olivier Giroud as one of two recognised strikers. At the other end, the double pivot of Jorginho and Mateo Kovacic will be essential in keeping Porto's counter at bay while Marcos Alonso or Ben Chilwell will have their hands full with Corona.

Prediction: With both legs played on neutral territory, the first leg will be a nervy affair with Chelsea and Porto battling out a draw, before Chelsea go on to win the return fixture next week. Tuchel knows what it takes to reach the final of the Champions League, having done that with PSG last season, and has the nous to steer Chelsea through this tricky tie. -- Tom Hamilton