The 2023-24 Champions League group stage is underway and Matchday 1 is wrapped up as Manchester City kick off their title defence, while Arsenal, Barcelona and Newcastle United return to the competition. After a thrilling first round of games, we asked our writers Gab Marcotti, Mark Ogden and Julien Laurens to answer some of our burning questions.

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Who are the players that impressed on Matchday 1?

Marcotti: Goalkeeper Ivan Provedel, not just for his late goal-scoring heroics, but because he kept Lazio in the game with a string of saves against a dominant Atletico Madrid. Shoutout to Barcelona loanee João Félix too, of course, Man City midfielder Rodri (is there anything he can't do?) and Arsenal's Martin Odegaard, who is quickly becoming one of the best in the world in his position.

Ogden: Aside from the obvious -- Man City's Julián Álvarez, Real Madrid's Jude Bellingham and Bayern Munich's Jamal Musiala -- I'm going to go with Red Star Belgrade forwards Cherif Ndiaye and Osman Bukari. Bukari scored the opening goal in a 3-1 defeat against Manchester City at the Etihad and playing as a forward against Pep Guardiola's side is a thankless task, but the duo's pace and movement was a constant threat. Their partnership could yet see Red Star sneak second spot in Group G and a place in the round of 16.

Laurens: Felix. After two games for Barcelona, against Real Betis and Antwerp, he has two Man of the Match awards. On his Champions League debut for the Blaugrana against Antwerp on Tuesday, he contributed two goals and an assist. He is happy, free from the defensive restrictions he had under Atletico coach Diego Simeone. If he can sustain this level through the season, Barcelona will be brilliant.

Who are the biggest threat to Man City's title defence this campaign?

Marcotti: Other than the obvious (injuries, refereeing, Guardiola doing something silly like dropping Erling Haaland and playing Éderson up front), there's nobody close to City right now. You have to imagine what these teams are going to look like in the spring. I think Barcelona have an exceptional keeper (Marc-André ter Stegen) who can dominate games and a ton of firepower up front ...if Xavi picks the right guys in the right game. As for PSG, they may have the highest ceiling of all the contenders, it's just a question of whether Luis Enrique can get a tune out of them and make them more than the sum of their parts.

Ogden: Even Guardiola's great Barcelona teams were unable to win back-to-back Champions League titles, so let's not hand the trophy to City this season yet. Bayern Munich, Real Madrid and Barcelona all have their faults, but they also have the players, coaches and super-club mentality to beat City in the latter stages of the competition. But it is only down to those three -- nobody else comes close.

Laurens: I like what Xavi is doing with this Barcelona team, as well as Inter's continuity under Simone Inzaghi and also what Enrique is building at PSG, but unless something dramatic happens, nobody will be able to beat Pep and City.

After 20 years, it's the first time that neither Lionel Messi or Cristiano Ronaldo are in the competition. Who do you think can fill the void they've left?

Marcotti: I don't know that anybody can fill the void, but I'd imagine PSG's Kylian Mbappé is best placed to do so. Why him and not Haaland? Because he's more charismatic and because he's asked to carry the team more than Haaland does. He has a new manager, a bunch of new teammates, etc. So I guess it's on him. But, really, we need to think long and hard before we mention anybody in the same breath as Messi and Cristiano.

Ogden: Mbappe, Haaland and Bellingham are the obvious candidates to be dominant players, but here's hoping that the post-Messi/Ronaldo era is a return to focusing on great teams rather than individual players. Neither Messi or Ronaldo could achieve their great feats without world-class teammates alongside them, but the likes of Xavi, Andres Iniesta, Luka Modric and Karim Benzema never got the credit they deserved. It's a team game, so let's celebrate the collective again.

Laurens: They will never be replaced. It's impossible. Instead of having two GOATs, we will have multiple young stars with Mbappé, Erling Haaland, Vinicius, Bellingham, Jamal Musiala, Gavi, Pedri, Khvicha Kvaratskhelia, Victor Osimhen and a couple more. That will almost fill the void.