Phil McNulty
BBC Sport chief football writer at Emirates Stadium

Arsenal know they must go for it - but with this all-out attacking approach and a defence stripped bare by injuries, they must also guard against fallng victim to the pace of Marcus Rashford and Anthony Martial.

It's a delicate balancing act but time is running out.

Image source, Reuters

Into the last 10 minutes of the 90 but again, we will have a shedload of extras added on. Should be at least eight.

Paul Pogba pokes a pass through into the run of Marcus Rashford, Petr Cech does well to spread himself and save - but Rashford was offside...

United have not had a shot on target other than their two goals.

Manjeet: Mourinho would have brought Jones and Fred on. Not Rashford and Martial.

Andy Townsend
Ex-Chelsea midfielder on BBC Radio 5 live

Ole has seen Koscielny has come off and thought now is the chance to put this game to bed. These calls are always so fascinating for managers to make, do you stick or go and get the third one to put it out of Arsenal's reach?

There's going to be a fourth goal in this game, surely. I have no clue which way it will go though.

If you're just tuning in there will be a lot of added time to this match, Laurent Koscielny was treated for about eight minutes for a head injury.

Jesse Lingard is booked.

Save! Arsenal come down their left for the umpteenth time, Ainsley Maitland-Niles wins the ball at the back post, Alexandre Lacazette gets the ball out from under his feet and hits a steaming shot which Sergio Romero beats clear.

United could be in straight away but Marcus Rashford can't control and play in Jesse LIngard. It's on a knife-edge.

Image source, Reuters

Jermaine Jenas
Former England and Tottenham midfielder on BBC One

Romelu Lukaku made a huge contribution, he's played well. Arsenal are only going to get more adventurous, leaving space for these two speed merchants. It seems Ole Gunnar Solskjaer thinks they need another goal to get through this tie.

Who cares?

Two changes for the visitors as Romelu Lukaku and Alexis Sanchez come off, Marcus Rashford and Anthony Martial come on.

Not ideal for Granit Xhaka and co.

Image source, Reuters

Arsenal are either going to score one of the goals of the season, a real 75-pass masterpiece like that Jack Wilshere one, or United are going to score on the break.

The battle lines are drawn. Arsenal have had 66% of the play since half-time.

Ashley Young is booked for handball, despite doing the classic 'hold your head' stance. Steven Taylor needs to give him some advice. The free-kick comes to nothing though.

Jermaine Jenas
Former England and Tottenham midfielder on BBC One

Aaron Ramsey's touch makes the ball bounce up which is perfect. He wants to cut across the ball. He knows his contact was not good enough.

Granit Xhaka is indeed playing at the back for Arsenal. They are caught on the break again, Paul Pogba fakes to shoot and instead looks to play the pass but overcooks it.

Arsenal come back downfield and Aaron Ramsey slices a shot over the top from 22 yards.

That was an eight-minute delay. We're doing our best to cause the editor of the News at Ten plenty of grief this month...

Laurent Koscielny can't carry on. That looks to be much more than just a cut, he looks like he can't open his jaw properly. Mind you on the replay Romelu Lukaku really caught him. Like being kicked by a horse.

Matteo Guendouzi comes on, and Mesut Ozil also replaces Alex Iwobi. Granit Xhaka to centre-back?

Image source, Reuters

What an effort that is!

Kasey Palmer steps up to take a free-kick from quite a distance, whips it comfortably over the wall and it smashes against the post.

That would have been some goal from the Chelsea loanee. He seems to be a real fan favourite already.