Ajax think they are ahead against Roma now but Dusan Tadic has a goal disallowed by the VAR for a foul. Roma still lead on away goals (2-2).

Granit Xhaka is penalised for a foul on the left and the hosts could look to hook this into the box... they do and Peter Olayinka gets up well, but can only send his header over the crossbar.

Almost. Donny van de Beek is heavily involved in this move with several give-and-goes. Bruno Fernandes crosses and Edinson Cavani shoulders the ball wide after it misses his head.

David Zima, the Slavia Prague centre back, finds himself in the box and manages to engineer a shot on goal, but there are plenty of blue bodies behind the ball to turn it behind.

Simon Stone
BBC Sport at Old Trafford

It is good to see Juan Mata warming up.

The popular Manchester United midfielder has struggled badly with injury this season.

Mata has been involved for just nine minutes in two substitute appearances since 9 January.

If you think you read an entry a couple of minutes ago saying Ajax are leading Roma on away goals, you definitely imagined it...

Ajax teenager Brian Brobbey runs onto a long ball and hit a clever first-time finish past the advancing Roma keeper. That makes it 1-0, 2-2 on aggregate, but Roma still lead on away goals. And we never said anything else...

One more Ajax goal would set up a United semi-final.

Bukayo Saka has been so good. He's pretty much dictating play from the right, getting on the ball and cutting inside, playing one-twos. Fully deserved his goal earlier.

Chances at both ends. Jorge Molina's header is deflected into David de Gea's path by Aaron Wan-Bissaka.

And then Mason Greenwood heads wide for United.

Alexandre Lacazette takes a tumble on halfway after being knocked off the ball from behind. Arsenal look to get it moving quickly and the lively Emile Smith Rowe wins a corner on the left.

Four changes for the hosts, who bring on Oscar Dorley, Lukas Masopust, Denis Višinský and Ondrej Lingr.

And away we go.

The second half begins.

United replace the booked Paul Pogba at the break. Donny van de Beek is on.

Granada bring on Antonio Puertas and Luis Suarez. Kenedy and Roberto Soldado are replaced.

Chris Waddle
Ex-Newcastle and England winger on BBC Radio 5 Live

Arsenal's young players have been their best players this season - Aubameyang and Lacazette have been hit and miss. The senior players have question marks against their name and the younger players have just gone out and played and that is why they are in the side because they are doing the business.

What frustrates you is why can't they play like this every week? Even if they lose you'd say they've put a shift in, created chances and looked like a team, it is when they are half at it they look poor. Tonight they have realised how big this game is and they have absolutely annihilated Slavia Prague.

Donny van de Beek is warming out on the pitch at half-time.

Mikel Arteta said before the game his Arsenal side had to be more efficient in front of goal and they certainly were in the first half.

Slavia Prague will need to score four without reply if they are to go through.

Chris Waddle
Ex-Newcastle and England winger on BBC Radio 5 Live

Arsenal have been brilliant. I'm like anyone else in the football world in having a question mark against them.

I said it was their biggest game of the season and they've played it like it is. They have thoroughly deserved their lead and Slavia Prague won't able to believe they are seeing this Arsenal side but it does show they have it in them.

And that's the break.

Arsenal in complete control of the tie after three goals six first-half minutes in Prague.

Arsenal almost release Alexandre Lacazette over the top but goalkeeper Ondrej Kolar is out quickly to gather before the Gunners forward can get there.

The half-time whistle goes. United are cruising into the Europa League semi-finals.

United overcomplicate this. Edinson Cavani flicks a lovely header into the path of Paul Pogba. Instead of shooting he lays it off for Bruno Fernandes and then he - instead of shooting too - tries to lift it over the top to Cavani but it runs out.