Ramsey slots home second from Ozil through ball
Mkhitaryan's first goal for Arsenal with shot across keeper
Return leg takes place in London on 15 March
That's the first and so far only goal of the evening across Europe after 15 minutes.
Atletico Madrid 0-0 Lokomotiv Moscow
Borussia Dortmund 0-0 Red Bull Salzburg
CSKA Moscow 0-0 Lyon
AC Milan 0-1 Arsenal
That's the first goal AC Milan, unbeaten in 13 games, have conceded in seven games - a run stretching over a month.
Henrikh Mkhitaryan
Moments after they could have conceded a penalty, Arsenal lead. Mesut Ozil plays a good pass over the top to Henrikh Mkhitaryan, who cuts inside onto his right foot - and his shot loops in off Leonardo Bonucci's back.
It's Mkhitaryan first goal since his January move from Manchester United.
Image source, Getty ImagesAC Milan 0-0 Arsenal
Well now. Has Hakan Calhanoglu's honesty cost Milan a penalty? Almost certainly yes.
Arsenal's defence switch off again and Calhanoglu has a free run towards the box. Gunners keeper David Ospina comes flying off his line - the Milan player tries to hurdle over him but loses his balance and the chance is gone.
Obviously I'm not advocating anything, but a lot of players would have found the contact there and taken a penalty.
Image source, ReutersAC Milan 0-0 Arsenal
Dreadful play by Arsenal. Callum Chambers gifts the ball to Hakan Calhanoglu and then Shkodran Mustafi comes charging out to close him down - leaving space for Patrick Cutrone to receive the ball and shoot wide. Let-off for the Gunners.
Image source, ReutersAC Milan 0-0 Arsenal
Arsenal are coming into the game more and Sead Kolasinac's cross is only half-cleared. It's end to end now. The game that all neutrals were hoping for.
AC Milan 0-0 Arsenal
First chance for Arsenal as Henrikh Mkhitaryan's shot from Jack Wilshere's lay-off flies into the side netting. Mesut Ozil was involved in the build-up with a cheeky nutmeg.
AC Milan 0-0 Arsenal
Arsenal defender Calum Chambers is down injured as he appeared to bang his head into Hakan Calhanoglu's body. Looks like he should be fine to play on after treatment.
AC Milan 0-0 Arsenal
Arsenal do break into the box now but Danny Welbeck concentrates so much on holding off his marker that he doesn't actually control a cross into the box - and Milan get it away.
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Andy Capontes: If Milan are half as committed as Gennaro Gatuso was as player then Arsenal will be in trouble! They need an away goal.
Looking at starting 11, AC Milan will not be shaking in their boots, worst starting 11 I've seen and the subs are hardly game winners.
Luke, Slough
As an Arsenal fan, I'm looking for a spectacular loss. No prospect of Champions League qualification will really give the board a decision to make with regards to Wenger. Here's to hoping!
Henry, Southampton
AC Milan 0-0 Arsenal
Alistair Bruce-Ball
BBC Radio 5 live at San Siro
Arsenal are under a lot of early pressure in a raucous atmosphere.
AC Milan 0-0 Arsenal
Milan almost lead as a cross is flicked on and Giacomo Bonaventura is inches away from turning it home at the back post. It's a corner - which Arsenal clear again.
But this is incessant attacks from Milan. Arsenal haven't really been past the halfway line.
AC Milan 0-0 Arsenal
Early corner to Milan as Patrick Cutrone's cross is deflected off Shkodran Mustafi. The Gunners get it clear.
Arsene Wenger will be praying his side don't concede early.
Cutrone wins another corner now.
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Competition for each position is what's lacking at Arsenal. Players who are playing badly are retained in the side! This current team won't scare anyone at this moment in time.
Matt, Winchester
As a Spurs fan, the only remedy for last night's heartbreak is watching this Arsenal side not even attempt to play football. Can't wait for the game!
Tom, London
Shanmugaraja CK: It's ridiculous to be so negative even before the match starts. Can we all just shut up, keep our criticisms out for 90 minutes and just get right behind the team?
AC Milan 0-0 Arsenal
Under way in Milan.
AC Milan v Arsenal (18:00 GMT)
Image source, Getty ImagesBefore all of tonight's Europa League games there will be a minute's silence in memory of Italy and Fiorentina defender Davide Astori, who died aged 31 at the weekend.
It is particularly poignant at the San Siro as Astori, whose funeral was held in Florence today, started his senior career with Milan.
Several Milan players, including captain Leonardo Bonucci, played alongside Astori for the Italian national side, while most of them played regularly against him in Serie A.
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Joe Wedgwood: Wanted to see Ainsley Maitland-Niles today in middle or left back. Sead Kolasinac built like a tank but not quite performing lately. But get behind Arsenal tonight boys! We need support!
Vivek lamsal: AC Milan vs Arsenal, here we go again. Pathetic fans calling Wenger out. Let the game begin, get behind players.
Richard Elgar: We're playing AC Milan at the San Siro. Matches like this should be why you're a football fan. Get a life and get behind your team!
AC Milan v Arsenal (18:00 GMT)
Here the players come. A large crowd at the San Siro welcomes them all out onto the pitch.
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Ryan Lloyd: Given that their only way of qualifying for the Champion's League next year is the Europa League, wasn't it a monumental oversight for Arsene Wenger to sell a good striker who was eligible for the Europa League (Olivier Giroud) and buy one who wasn't eligible (Pierre-Emerick Aubameyang)?
Christopher M. Selby: Arsenal 6-1 tonight.
Terryfic Otobong: I will be watching this game with my heart. I'll be praying under my breath. Arsenal really needs to win.
We'll also be bringing you updates from the other three games which kick off at 18:00 GMT.
Atletico Madrid v Lokomotiv Moscow
Borussia Dortmund v Red Bull Salzburg
CSKA Moscow v Lyon
And we'll keep this live page going after the Arsenal game for the four 20:05 GMT matches (as well as Gunners reaction).
Lazio v Dynamo Kiev
Marseille v Athletic Bilbao
RB Leipzig v Zenit St Petersburg
Sporting Lisbon v Viktoria Plzen