Arsenal have had 15 shots (inc. blocks) in this game; their most in the first half of a game without scoring since December 2017 against Manchester United (also 15).
Playing at home against 10 men, Arsenal surely must win here. Despite their frustrations with the referee, Atleti will be the happier of the two sides right now.
There have been chances at either end, but Oblak and Ospina are holding their own right now.
It's goalless at the break, but that first half was not without drama. Vrsaljko was dismissed early, before Simeone was sent to the stands.
45' + 2' HALF-TIME: Arsenal 0 Atletico Madrid 0
45' + 1' The ball drops for Ramsey at the back post. Another big block, this time from Thomas. Arsenal want a goal before the break.
45' Corner at the other end. Mustafi picks out Bellerin, who is challenged as the ball runs behind. Two minutes of stoppage time.
44' OVER! Correa darts into the Arsenal area on the left, turns inside and beyond Mustafi, then blazes over the top. A half-chance.
43' Arsenal players are lining up to shoot in the area, but the players get in one another's way. Atleti clear and then the entire visiting back line dashes across to berate the referee following another foul.
41' SAVE! The ball drops for Correa to flick a cross in from the right, allowing Gameiro to go for goal with his head from a good 15 yards. Ospina holds and then batters a pass out to Lacazette. The pass at the other end is poor, though.
40' More Atleti complaints. Mustafi fouls Griezmann. The visitors have a free-kick 40 yards from goal.
39' It's Xhaka's turn to go for goal for Arsenal with a curler. High and wide. Nowhere near.
38' Arsenal simply cannot afford to concede the first goal here and, given the circumstances, they have no excuse to either. It remains goalless, 11 against 10.
37' SAVE! A vital stop from Ospina! Some more careless Arsenal passing allows Thomas to take possession, charging past challenges and into the area. He tees up Griezmann, but a powerful drive is well parried by Ospina.
36' Xhaka lofts an optimistic ball in behind the away defence for Welbeck, but Oblak is quickly off his line to claim. Good goalkeeping.
34' Welbeck feeds a pass for Bellerin in the area, but the Spaniard pulls out, perhaps hoping to win a penalty from Hernandez, who is steaming in. The Atleti man wins the ball, which appears to have deflated. New ball, drop ball and Atleti have it back.
33' SAVE! Now there's an opening! Griezmann finds space on the edge of the area and hits a dropping ball hard and low. Good save from Ospina, who holds on.
32' A couple of errors creep into Arsenal's play in their own half and Atleti are able to attack for a period. No chances as of yet for the visiting 10 men.
31' WIDE! Lovely play from Arsenal and Monreal hammers wide. The hosts are probing in front of the Atleti defence, before Ozil's incision has the Spanish side scrambling. Ramsey crosses, Lacazette flicks on and Monreal volleys across goal.
29' Is Thomas fortunate to escape a yellow card? He wins the ball ahead of Monreal, but his boot is very, very high. Just a free-kick.
28' Lacazette again flicks on at the near post! Ramsey hammers the ball back across goal, but Atleti clear.
27' Brilliant from Lacazette! Thomas' pass is intercepted, with the France forward then darting into the box and nutmegging a defender. His cross is cleared, but Arsenal soon have a corner...
26' Atleti have the opportunity to launch a ball forward from a free-kick. Gimenez is caught offside. That's poor.
25' Ozil goes for goal from 20 yards. Curled high and wide. Arsenal keep pushing.
23' APPEAL! Lacazette wants a penalty... He turns once, twice, three times in the area and then goes to ground under pressure from Godin. It looks speculative.
22' A lax Monreal pass almost lets Koke in, but Arsenal quickly have the ball back. The hosts must remain patient.
21' CHANCE! Now Koscielny should score! Lacazette flicks on the corner and it drops for Koscielny at the back post, but he slices wildly at the volley. Well wide.
20' SAVE! What a stop from Oblak! Wilshere feeds Welbeck, who shoots hard and low. The goalkeeper stands up to block. Corner. Arsenal are rampant.
19' Vrsaljko's sending off was the earliest in a game in Europa League history (9:09).
18' SAVE! More nice build-up play from Arsenal. Welbeck crosses and Wilshere nods tamely straight at Oblak.
18' BLOCK! Vital from Godin! A slip-up in the Atleti back-line looked to have let Ramsey in, but the defender got across to lunge into a block.
17' Bellerin delivers another good cross from the right and Thomas, covering at right-back, heads away. Arsenal build again.
16' Now the hosts enjoy some possession. They can take their time, but it is important now that Wenger's men win this and keep a clean sheet. This is a huge opportunity.
14' Atleti have responded strongly, trying to push the ball forward. Arsenal had dominated early on but they are yet to use the red card to their advantage.
13' OFF! Simeone is gone, too! This is incredible early drama. An Arsenal foul went without a booking and the Atleti coach is furious. The referee, understandably, has had enough and sends him to the stands. That is a brave call, even if it appears to be the right one.
11' Vrsaljko is taking his time to disappear down the tunnel. Simeone is waving his arms in dismay. Atleti feel hard done by - they shouldn't.
Š. Vrsaljko
Yellow 2nd/RC
10' RED! Wow! A second yellow card for Vrsaljko and what a blow for Atleti. The right-back is late on Lacazette and catches the forward's ankle. It looks to be a great decision.
9' Danger at the other end! Thomas' pass is timed well for Vrsaljko to run down the flank and cross, but Mustafi is there to nod clear when Gameiro cannot quite stretch to make contact.
9' SAVE! A simple one for Oblak this time. Welbeck, influential so far, cuts inside from the left and shoots low into the goalkeeper's hands.
8' The crowd are in good voice early on. Arsenal are quickly back on the ball and attacking again.
7' SAVE! Lacazette again from a cross on the left! Welbeck and Monreal combine, delivering for Lacazette to head for goal. Oblak is alert to parry. Smart reactions.
6' CHANCE! Huge opportunity for Lacazette! Arsenal have started really well, pressing the opposition and eventually feeding Welbeck on the left. A glorious cross picks out Lacazette unmarked, but his downwards volley flies wide.
5' Dangerous cross from Bellerin! Xhaka fizzes a pass into Ozil, who nudges the ball onwards. The right-back crosses, but Vrsaljko, on the far side, is able to nod clear.
4' Ozil delivers, but Atleti clear at the second attempt. Gameiro looks to lead a counter-attack but can only pick out a recovering defender.
3' Corner to Arsenal. Koscielny picks out Bellerin on the right, and the Spaniard runs inside and then out, winning the set-piece from Hernandez.
Š. Vrsaljko
Yellow Card
2' YELLOW! A very early card for Vrsaljko. Gimenez undercooks a pass and allows Welbeck to intercept, before the Atleti right-back chops down the onrushing Wilshere.
1' Arsenal give the ball away swiftly and the visitors look to attack down the left. Ramsey is across to challenge.
1' KICK-OFF: Lacazette gets us under way!
Here we go! The teams are emerging from the tunnel...
The crowd at Emirates Stadium is a sea of red and white, with the home fans waving shimmering flags. The away supporters, adorned in the same colours, have scarves and banners of their own. The players will be with us shortly.
Diego Simeone added: "I hope we can play with a mental freedom in a stadium where Arsenal are very strong. You need courage to get into a final."
Atletico Madrid have scored 15 goals in their six Europa League games this season, giving them the best goals-per-game average in the competition (2.5).
"[Arsenal's] players deserve something special," Wenger said ahead of this one. "I want to [win the competition] for them. My biggest satisfaction would be to achieve something with the group of players I have."
Arsenal are appearing in their eighth European semi-final – they have progressed from six of the previous seven, only failing to reach the final in 2008-09 in the Champions League when they lost to Manchester United.
Positive news for Arsenal, as Wilshere and Ozil are both available from the start. Atletico's Costa is only fit to make the bench.
Subs: Axel Werner, Fernando Torres, Gabi, Stefan Savic, Diego Costa, Vitolo, Roberto Olabe.
Atletico Madrid (4-4-2): Jan Oblak, Sime Vrsaljko, Jose Gimenez, Diego Godin, Lucas Hernandez, Angel Correa, Thomas Partey, Saul Niguez, Koke, Kevin Gameiro, Antoine Griezmann.
Subs: Petr Cech, Rob Holding, Alex Iwobi, Calum Chambers, Ainsley Maitland-Niles, Sead Kolasinac, Eddie Nketiah.
Arsenal (4-3-2-1): David Ospina, Hector Bellerin, Shkodran Mustafi, Laurent Koscielny, Nacho Monreal, Aaron Ramsey, Granit Xhaka, Jack Wilshere, Danny Welbeck, Mesut Ozil, Alexandre Lacazette.
Let's get the team news ahead of this first leg...
The Spanish outfit have won only one of their last five matches in all competitions, though, with Arsenal dominant at home in recent weeks.
Will Arsene Wenger bow out with a European trophy? He must first overcome an Atleti side also chasing their only silverware of the season.
Hello and welcome to our live text commentary of the huge Europa League semi-final first leg between Arsenal and Atletico Madrid at Emirates Stadium!
