Saturday marks the second and final clash between longtime Spanish rivals Real Madrid and Barcelona for the 2020-21 season. Real hold the edge, having won convincingly 3-1 in November, but Barcelona are unbeaten in La Liga since Dec. 5 and hold the upper hand in the title race -- quite a turnaround for a side in crisis at the beginning of the season, with Lionel Messi wanting to leave and the squad in disarray around him.

It's one of the biggest games in world soccer, and Saturday has two big storylines to watch. ESPN's experts break down the game.

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Barcelona: Enjoy Messi, if this is indeed the end

Right now, it seems certain that Lionel Messi is revitalised, happy, evangelically recommitted to Barcelona -- as certain as it was last August that he would be, at any cost, leaving FC Barcelona. Relations are at the point that, by May or June, it seems realistic that he will announce he's staying at Camp Nou under a new contract. But that's the point.

It seemed 100%, cast-iron certain just a handful of months ago that everything was broken, that Messi was sick to the back teeth of being surrounded by mediocrity and mendacity, and yet here we are. A full 180-degree pike, with triple salchow, change of attitude and all it requires now is what any person in sales will tell you is the hardest part: closing the deal.

For those reasons, it's obligatory to mark this weekend's Clasico by saying that if there were another reverse-flip, if Barcelona somehow displeased him with their inability to sign new talent or in their capacity to offer him the right remuneration over the next two or three years -- lots of ifs and buts -- or if it turned out that there's something special on offer at Manchester City or PSG, then this would be his last chance to play Real Madrid in blaugrana colours.

Whichever side of the Clasico divide you find yourself on, it's a sobering thought even for us neutrals. Sixteen years of Messi vs. Madrid, and his magic-on-demand, have flitted past us like countryside images out the window of a high-speed train. Gorgeous and imprinted on our consciousness, but gone far too soon.

For the good of this fixture, for the nourishment of La Liga and, unquestionably, for the benefit of FC Barcelona, who are fundamentally committed to keeping their in-house genius, let's hope that win, lose or draw, we see the nimble, dancing, scheming legend from Rosario, Argentina gliding and dribbling across the Camp Nou and Santiago Bernabeu pitches many more times in classic Clasicos.

But if not, what are we left with? His impact has been gargantuan; that's the only word for it. It should probably go without saying that Messi has faced no other rival as many times as he's played Real Madrid, one of the two clubs that was hovering in hope when, back in 2001-02, negotiations between Barca's slow directors and his father, Jorge, were turning sour.

Just as Spain's FA made tentative moves to discover whether Messi wanted to play for La Roja instead of Argentina -- Messi was appalled by the idea -- Madrid were primed and ready to pounce when, finally, a couple of Camp Nou men woke up to the fact that they absolutely had to find a way to retain this 13-year-old whose massive talent outsized his tiny frame.

And once they failed to get him, Madrid became a foil. From his Clasico debut, one sharp, tangy November evening in Spain's capital nearly 16 years ago, until this weekend at an empty but nonetheless iconic Alfredo Di Stefano stadium in Madrid's superb training complex, if Los Blancos didn't exist, Messi would have had to invent them.

"I'm Argentinian, but I feel very Catalan," said Messi in a recent sports paper interview in Barcelona. It showed, too.

I was at his debut against Madrid, sitting next to my friend John Alexander, whose ticket in the section reserved for friends and family of Real Madrid players had "from Zinedine Zidane" stamped on it. I'd ducked work duties and was just there to savour it -- little did I know there would be a clever, confident cameo performance that, though dwarfed by Ronaldinho's two brilliant goals in a 3-0 win that night, would endure long past the Brazilian's sell-by date.

Messi was an imp that night. He cared not a jot for the stage or the baying Real Madrid fans; he wasn't put off by the racist abuse that both Samuel Eto'o and Ronaldinho suffered, nor could Madrid's players subdue him. Two Clasicos later, the seeds that were sown in his first game against Real Madrid flowered with a hat trick at Camp Nou, as when Barcelona's 10 men (with defender Oleguer red-carded) wrested a 3-3 draw against a thunderously powerful, Ruud van Nistelrooy-inspired Madrid.

The stories and the images go on, and on. But for once, the stats actually tell a good tale.

Before the era of Xavi, Andres Iniesta, Pep Guardiola the coach, Carles Puyol, Gerard Pique, Messi, Ronaldinho, Eto'o, Sergio Busquets, Neymar and Luis Suarez, it's not that Barcelona couldn't beat Real Madrid -- it's just that they didn't do it all that often. The all-time Clasico scorecard was heavily balanced in favour of Los Merengues.

No more; the head-to-head stats are as tight as the seals on a submarine's portholes. The trophy count, particularly in La Liga and the Champions League, has metamorphosed. And notwithstanding all the brilliant talent I mentioned, along with a dozen more essential, exceptional cameo role players, the number one catalytic element, by far, has been Messi. Why not, he's a genius? Which is why, ahead of this weekend, it's a little strange to break down Messi's Clasico numbers.

Like I said, he and Madrid are like Sherlock Holmes and Professor Moriarty, Superman and Lex Luthor, Roadrunner and Wile E. Coyote, Tom and Jerry. (Please note, who's the hero and who's the baddie depends wholly on which club you support: the roles are fully interchangeable!) This 33-year-old Argentine, born some six-and-a-half-thousand miles from the Spanish capital, has imposed himself on the fixture. Nobody, including his compatriot (Di Stefano), after whom this weekend's stadium is named, has scored more goals when Real Madrid and FC Barcelona do battle. Ever.

Messi's overall stats against Barca's mortal rivals: played 44, won 19, drawn 11, lost 14, 26 goals, 14 assists and 11 yellow cards.

What do you reckon about those figures? Less impressive than you remembered? Stunning because it's against one of the best, most ambitious, most "winning" clubs in football history? What's your take?

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One of the standout facts, I reckon, is that one way or another, Madrid have increasingly got his measure in recent seasons. Against Los Blancos, Messi has "only" scored five times in their past 17 meetings. He's not hit the net in a Clasico for three years now and it's four years since Messi scored while winning a Clasico in La Liga.

Hmm. Interesting, no?

It's linked that six of the 14 defeats Messi has suffered against Real Madrid (roughly half) have come in those past 17 matches, in which he's only managed to score five times. (By the way, Karim Benzema has scored five goals across his last 19 Clasicos, just to put Messi's slight drought in context.) It may well be that this little marvel is the most dominant figure in the history of a beautiful, dangerous, culturally volatile fixture, but his win rate is less than 50%!

Of the 23 other club opponents Messi has faced 10 times or more, his win rate is usually much higher than that, hovering around 80% in most instances. Against no other opponent, whether club or country, has Messi lost a double-digit number of games. Next closest is Atletico Madrid, against whom he's lost eight of 42 meetings while winning 24. Against no other opponent has Messi had more yellow cards (11), either.

It is, I think, a picture of how this Herculean talent used to hit Madrid like a hurricane, often left opponent coaches and players in smithereens, but has gradually been reigned into a status closer to a small storm as Madrid built defences, prepared better and began to understand what to expect. And in my mind, it's not just about Messi ageing or the Barcelona squad declining. It's kudos to Real Madrid for working out the answer to "how do you solve a problem like La Pulga?"

You can take it to the bank that Barcelona's No. 10, who just became their all-time leader in appearances -- to accompany all his other all-time achievements -- is obsessed with winning the league and Copa del Rey double this season. He knows better than anyone that despite his renewed appetite for life at Camp Nou, the deal to stay is never definitive until terms are thrashed out and the ink is dry on a bumper contract.

The thought of another trophyless season, even more so if this were to be his last in Catalunya, is utterly abhorrent to him. Did you see his evangelistically joyful celebrations when Sevilla were defeated in the Copa semifinal at Camp Nou last month? Or the huge, emotional leap into Ousmane Dembele's arms when the Frenchman scored a last-minute winner against Valladolid at Camp Nou on Monday?

This Saturday's Clasico, as part of the route to what might become Messi's 11th Liga title, will have him as tense, as hungry and as filled with competitive adrenaline as any he's played in since the 2011 Champions League semifinal first leg when, it turned out, he gave probably his all-time, signature performance.

This meeting happens against a backdrop of Madrid having won, clinically and deservedly, at Camp Nou last autumn, Madrid being the defending league champions and Madrid owning the head-to-head record this season that would automatically make them champions if the two sides finished equal after 38 games. It also comes against a backdrop of Messi having looked sluggish and short of cutting-edge crispness against Valladolid, having gone over two weeks without a match during the international break.

It's not an arithmetical fact, but the suspicion lingers that unless Barcelona can win this test against their (and Messi's) favourite rivals, the league title may just be beyond them. It is a fact, however, that since December, Ronald Koeman's Barcelona have intermittently played the most thrilling, most electric and smartest football of this strange La Liga season. Can they convert that to a seismic result when the chips are down?

Whether or not this happens to be Messi's last joust with his eternal rival, and given that one of his chief tormentors, Sergio Ramos, isn't playing, will the Argentine's inherently voracious instincts mean we are in for a Clasico masterclass in which he torments Real Madrid with his old majesty?

Saturday brings another Clasico in the Messi era. Intriguing, intense and unmissable, but hopefully not "adios, maestro." -- Graham Hunter

Real Madrid: It's not just about Messi, but his longtime rival, Sergio Ramos

You know who won't miss Messi if he goes? Real Madrid. Oh, wait, actually that's not right. Or at least not entirely.

In the history of the Clasico (which wasn't always called the Clasico), only Di Stefano and maybe Johan Cruyff have done as much to tilt the power balance toward one of these great, historic rivals. And Cruyff had two chances, as player and as manager, to do it.

If Messi scores at the weekend, or indeed any weekend between now and the end of the season, it will be the thirteenth season in a row that he's scored at least 30 goals. No one has had a prolonged run of success like it -- not even Di Stefano, not quite. No club has lorded it over the league and the cup like Barcelona have with Messi.

He's won 10 league titles and that, of course, means 10 league titles Real Madrid haven't won, at a time -- let it not be forgotten -- when they too have had some of the best players in the world.

Just look at the stats Graham has outlined there. Or listen to Ramos, Madrid's captain. "Without Leo, we would have won more," he says.

It's simple, but it's true.

Ramos knows that well; he knows the danger, has felt the hurt. Messi has felt it too, quite literally. Remember in 2010, when Barcelona won 5-0 and the last thing Ramos did was run over and boot him into the air -- not so much a tackle, as an assault -- and one so premeditated that the referee that day, Eduardo Iturralde Gonzalez, could see coming. "It was one of those you can 'smell,'" he recalled. "I saw him running towards Messi and I thought: 'He's going to whack him.'"

Which he did.

Ramos would want rid of Messi, you would think. And yet, when it looked like the Argentine was about to go this summer, he insisted that there was no need for Messi to leave. "We'd like him to stay here," Ramos said. "He makes his team better, the league better, and the Clasico nicer."

Saying so underlines his own success, Madrid's success; maybe it makes sense. Maybe it's even selfish as much as it is admiration. After all, facing the best makes you better, and beating the best makes success even greater. True rivalries are built on this. Ramos knows that too, and was explicit about it: "It's good for those of us who like to beat the best," he said.

And yet, Ramos has never had any doubts that "the best" meant Messi. The Madrid captain even took on the late Diego Maradona when he had criticised Messi, saying that the 1986 World Cup-winning captain was "light years" behind his countryman. In a recent interview, Ramos even said that he would "100%" like Messi to join Madrid if he had to leave Barcelona. He would put him up at his house if it helped.

Yeah, nice try, Sergio. But it is true that Messi's departure would take something from this game. It's true, too, that Ramos' absence would as well.

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And this is the other element in play here. Madrid's captain is injured and will be unavailable on Saturday, though he will be at the game as ever, his voice booming around. If Messi may be about to play his last Clasico, Ramos may have already done so. His contract is up at the end of the season, and while it always feels like there can't be any outcome other than him and the club agreeing a deal to keep him there -- "the best thing for the club is that Ramos stays, the best thing for Ramos is that Ramos stays," teammate Nacho said this week -- he still hasn't renewed and his relationship with them isn't good.

Maybe he could go to Barcelona instead, then?

Without Messi, Madrid would have won more, and yet they come into this game knowing that they can't really afford to lose. That's the bad news; yet it's also the good news.

Here are two lists:

- Liverpool, Atalanta (twice), Atletico Madrid, Sevilla, Inter Milan, Barcelona
- Alcoyano, Levante, Shakhtar Donetsk (twice), Alaves, Cadiz

Guess which one is the list of games Madrid have won, and which is the list of games they lost?

OK, so you knew that one, but it's still quite something to lose to all of those teams in the second list. As is the fact that they didn't beat Elche or Osasuna either while they haven't lost to any of the big teams. And yet, when it mattered, Real won. Against the bigger teams, they won. As they always seem to do.

Last year, Zidane had been on the verge of the sack before Christmas, and he went on to win the league. This year, the same thing happened: In December, he was on the way out. He had just "hours" left in the job, El Mundo claimed. Madrid had won less than half of all their games, faced elimination from the group stages of the Champions League for the first time ever, and a huge week lay ahead, with must-win games against Sevilla, Borussia Monchengladbach and Atletico.

They won all three.

They have to win this Clasico too, and as ever, the obligation is an opportunity.

Madrid come into this game clinging to the hope of winning the league, which just three or four weeks ago seemed impossible. So do Barcelona. For much of the season, a title didn't seem likely for either of them. Atletico were too far ahead. Now, the gap is tiny: a single point from Barcelona, three above Madrid. Atletico have opened the door, and the wolf is there. Two of the fanged devils, in fact.

Neither of these teams are top and yet it still feels like that the one who wins will emerge from this weekend as favourites. Madrid have lost just once in 19 league games. Barcelona have lost none in 19. Atletico have won only three of their past eight. It's huge, but then it always is. It may be decisive, but then it's almost always that too.

It may also be the last time we see either of these men: Messi on the pitch, Ramos up in the stands. And you can guarantee -- absolutely guarantee -- that Ramos will seek out his nemesis from Rosario at the end. You can't help thinking that they'll be back. You can't help hoping so too, that all of these words here are worthless -- yeah, sorry about that, but plus ca change and all that -- and that with any luck, we can do it all again next year. Because when eventually they go, a generation will go with them.

Madrid fans will miss Ramos. They, like him, might even miss Messi too.

Well, sort of. -- Sid Lowe