A good game in Spain. Barcelona's Fermin Lopez, with a real chance to make a name for himself tonight, gets a shooting chance, but drags it well wide of the left-hand post.

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Theo Walcott
Former Arsenal and Southampton forward on BBC Radio 5 Live

Porto are already trying to slow the tempo down, they have almost killed the momentum of that opening five minutes.

That is the experience we were speaking about before the game, they are just using those tactics and taking their time to slow things down.

Alex Howell
BBC Sport at Emirates Stadium

The Porto side are already starting to take their time with getting the ball in play. There's been two throw-ins already that they have taken a while with and the home fans aren't happy.

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Kai Havertz closes down a cross and is met by a roar from the home fans.

But Havertz is penalised shortly afterwards for leaving an elbow in as he goes up for a header in midfield. Free-kick to Porto.

Victor Osimhen with a glorious chance for Napoli. It's just the man the Italians would want with the opportunity as he is through with only Marc-Andre ter Stegen to beat.

But with Barca defenders rapidly tracking back and closing the Nigerian down, the ball gets stuck under his foot and he can only prod the strike at the Barca keeper.

Osimhen may have been offside anyway after all that.

Matthew Upson
Former England defender on BBC Radio 5 Live

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Cracking tackle.

It was a brilliant challenge really from Wendell, went with the outside of his boot and crunched into Bukayo Saka, who had cut inside with the intention to shoot.

The cross then comes in from the left and is headed over the top of the bar. Good and intense attacking start from Arsenal.

Galeno launches a long throw-in for Porto but it's comfortably cleared by Arsenal.

Jorginho finds Bukayo Saka and he drives through the middle.

Wendell comes sliding in with a big challenge, the referee plays on and it's dinked towards the back post for Ben White.

He nods it just over the bar.

Good attack from Arsenal.

Victor Osimhen and Robert Lewandowski were the goalscorers in the first game in Italy and both have an early sniff of a chance at either end of the pitch.

Lewandowski just can't get a head on a delightful rabona cross from ex-Leeds man Raphinha. Wonderful skill.

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Phil McNulty
BBC Sport chief football writer at Emirates Stadium

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Arsenal manager Mikel Arteta asked the supporters to bring noise, passion and energy. All those boxes are being ticked, with a spectacular light show before kick-off to spice things up a little more.

A thick pall of smoke hangs over Emirates Stadium as the game gets under way with Porto fans brandishing flares. Their supporters are not exactly under-stated either.

Porto fans have made their presence known with a few flares and the mist is still blowing across the pitch as the teams kick-off.

Mikel Arteta is already on the edge of his dugout shouting instructions.

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Here we go then. Kicking off at the Emirates and Montjuic.

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Alex Howell
BBC Sport at Emirates Stadium

The atmosphere inside the stadium is excellent.

The home supporters just sang 'North London forever' which is the anthem they play before every home game.

The fans believe that Mikel Arteta and Arsenal can turn this around.

Arsenal XI: Raya, White, Saliba, Kiwior, Gabriel, Rice, Jorginho, Odegaard, Saka, Trossard, Havertz.

Subs: Ramsdale, Hein, Tomiyasu, Soares, Zinchenko, Elneny, Partey, Vieira, Smith Rowe, Nelson, Nketiah, Jesus.

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Porto XI: Costa, Mario, Pepe, Otavio, Wendell, Varela, Nico, Pepe, Conceicao, Evanilson, Galeno.

Subs: Ramos, Pedro, Cardoso, Sanchez, Grujic, Eustaquio, Jaime, Baro, Borges, Taremi, Namaso, Martínez.

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Barcelona XI: Ter Stegen; Kounde, Cubarsi, Araujo, Cancelo; Lopez, Christensen, Gundogan; Yamal, Lewandowski, Raphinha.

Subs: Pena, Astralaga, Inigo Martinez, Joao Felix, Romeu, Roque, Sergi Roberto, Casado, Hernandez, Guiu, Fort.

Image source, Opta

Napoli XI: Meret; Di Lorenzo, Rrahmani, Juan Jesus, Rui; Anguissa, Lobotka, Traore; Politano, Osimhen, Kvaratskhelia.

Subs: Contini, Gollini, Natan, Olivera, Simeone, Cajuste, Ngonge, Lindstrom, Mazzocchi, Ostigard, Raspadori.

Image source, Opta

Matthew Upson
Former England defender on BBC Radio 5 Live

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Martin Odegaard doesn't necessarily exude what you expect from a captain. It is an interesting choice. But he leads by example on the pitch.

You can lead in many different ways, you don't have to be pumping your chest and shouting, body language, presence and all the rest of it are important.

His consistency has been superb, he does it in his own way.

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Martin Odegaard says his experiences at Real Madrid have made him "a stronger and better player".

The Norway midfielder joined Madrid as a 16-year-old in 2015 but, despite becoming the club's youngest ever player, did not play regularly and was loaned out to Dutch clubs Heerenveen and Vitesse before successive seasons on loan at Spanish side Real Sociedad.

"I always believed that I was going to make it," said Odegaard.

"To play big games in the Champions League and games in the biggest leagues - I always had that belief.

"Football doesn't always go how you expect. When I signed for Madrid the plan wasn't for me to go on loan - but that's football and that's life.

"That's what I've done well: I've dealt with everything and worked hard.

"It's all part of your journey. You have to deal with it and everything I've been through has made me stronger and a better player."

Rezaa: Disgusted that some Arsenal fans would be okay with being elimated tonight. Big teams fight for all trophies. You don't see man city and Liverpool settling for just one trophy.

Linus: The number of Arsenal fans I'm seeing saying they'd be happy if we went out tonight is disgraceful. Weak mentality that we need to stop having if we want to be on top again. Yes Premier League is a focus, but UCL should be too. Don't put all your eggs in one basket

BBC Radio 5 Live

New York Times chief soccer correspondent Rory Smith believes Arsenal's Kai Havertz "has always been cursed by his versatility".

Havertz, who headed in Arsenal's late winner against Brentford on Saturday, has scored eight Premier League goals this season, having played in a number of different roles.

"He's able to play in lots and lots of different positions in lots of different ways," Smith told BBC Radio 5 Live's Monday Night Club.

"That makes him a bit of a Swiss army knife for a manager, which is a really useful trait.

"It is the sort of thing that means you play a lot of football but it doesn't necessarily mean you're in a position to showcase your best abilities."