Lorenzo Pellegrini just underhits a pass to Edin Dzeko in the box and then Chris Smalling hammers over the bar. This is a very entertaining game.

Roma have a bit of a break from the United pressure and win a corner as Scott McTominay slices a clearance from Rick Karsdorp's cross.

United clear the corner.

Villarreal string an attacking move together for the first time in this second half and it's Samuel Chukwueze who turns smartly to get a shot off, but it's saved well by Bernd Leno.

Matty AFC: We all knew Ceballos was going to be sent off but how on earth is that a yellow card?!

Chris Lord: Should have been subbed off at half-time, your mistake Arteta no point complaining about it.

Craig Smith: How many managers would have watched that first half performance and made no tactical or personnel changes?? #Arteta, external leaving this way too late to make changes!

Where was this United performance in the first half? Paul Pogba finds Scott McTominay, who sneaks in behind. He's only six yards out but tries to drag it across the box instead of shooting and Roger Ibanez gets a touch before Edinson Cavani can tap home.

Emile Smith Rowe is pretty much playing as a false nine at the moment, although after that sending off it may be more of an eight-and-a-half... he takes a knock but is quickly back to his feet.

United really are knocking on the door. Bruno Fernandes plays a fine outside-of-the-boot cross into the box which Roger Ibanez heads behind before Marcus Rashford can pounce.

Neil Lennon
Former Celtic manager on BBC Radio 5 Live

Now they are penetrating. That should have been another goal. Lovely cut back by Luke Shaw.

Oh dear. That's a huge blow for Arsenal.

Dani Ceballos is shown a second yellow card and he's off. Is he a touch unlucky? He's just narrowly beaten to the ball by Daniel Parejo and ends up standing on the Villarreal man's foot.

The Gunners down to 10 with just over half an hour of the first leg to go.

Image source, Getty Images

United have a chance to take the lead - they've been much better since the restart. Luke Shaw cuts the ball back from the left, it's past Bruno Fernandes but reaches Edinson Cavani, who rifles over the bar.

Another neat delivery from Martin Odegaard but the only player he has to pick out is Nicolas Pepe, who's drifting away from the far post. Juan Foyth gets across quickly to cover.

Emile Smith Rowe looks to take matters into his own hands and wriggle into the box with a driving run, before a loose touch sees it trickle out of play.

Simon Stone
BBC Sport at Old Trafford

That was a really important goal for Manchester United, you could tell that from Ole Gunnar Solskjaer's double fist-pump reaction to Cavani's shot hitting the net.

Not long after a mistake from David de Gea that could have been catastrophic.

United midfielder Paul Pogba is booked for fouling Roma's keeper... but a replay shows that's harsh.

Roma keeper Antonio Mirante rushes off the line and catches the ball, maybe Pogba's arm touches him but he goes down holding his head (which Pogba definitely didn't even touch).

Roma's Gonzalo Villar goes into the book for a foul on Paul Pogba. He slides in, wins the ball but catches Pogba on the shin in the follow-through.

The Arsenal pressure and possession is building, but Villarreal seem quite happy to sit in and nod everything away that comes into their penalty area.

Neil Lennon
Former Celtic manager on BBC Radio 5 Live

Magnificent. What a ball from Pogba, beautiful run from Cavani. It is all one touch and that is what was missing in the last half of the first half. That is so much better from Manchester United. Delightful goal. Delightful.

Neil Lennon
Former Celtic manager on BBC Radio 5 Live

He [Roma boss Paulo Fonseca] is going to end up with 10 players. It is one of those sort of very rare things that happen in football but maybe there was a discussion at half time.

United get a bit lucky again as Henrikh Mkhitaryan picks out Lorenzo Pellegrini in space in the box but he can't control.

Simon Stone
BBC Sport at Old Trafford

A quarter of the way through this tie and it is not going to plan for Manchester United.

Ole Gunnar Solskjaer has lost four semi-finals as United boss already. He really doesn't want to make it five.