Phil McNulty
BBC Sport chief football writer at Old Trafford

Jose Mourinho had every right to be aggrieved at that penalty refusal. Clumsy from Nacho Monreal in a very dangerous position.

Mourinho is really ticking now after some of referee Andre Marriner's decisions - but he can be happier with his team because they are looking far more dangerous than Arsenal.

Image source, Reuters

Mark Lawrenson
Former Liverpool defender on BBC Radio 5 live

This isn't the greatest game you've ever seen but it's definitely intriguing. Although Mark Chapman's just shot me a dark look for saying that.

Alexis Sanchez, nominally Arsenal's centre-forward, spends a lot of time deep in midfield. He has Mesut Ozil, Mohamed Elneny, Aaron Ramsey and Theo Walcott all ahead of him at the moment. 

John Murray
BBC Radio 5 live commentator at Old Trafford

We've seen an angle on the replay from behind and that's the view Andre Marriner had. But you can still see Monreal's arm come across Valencia.

Mark Lawrenson: No, I have to say in that position, it's quite natural. No penalty.

Image source, Reuters

Antonio Valencia has been the best player on the pitch on his return and another lung-buster down the right ends up at the feet of Anthony Martial on the left. He's been anonymous but the Frenchman drills in a very good effort which Petr Cech has to push over. From the corner Martial tests Cech again from range. Again he saves. 

Dennis Ethan: Mourinho has found an excuse should United go on and lose this match. 

Richard: HOW IS THAT NOT A PENALTY!??!   

Nii: No pen in a million years, Jose!

It's divided the pundits and the punters alike. Jose Mourinho will not let that one go, surely?

"I repeat, minute 35..."

John Murray
BBC Radio 5 live commentator at Old Trafford

What a save by Petr Cech, superb work down low to his left but it's superb from Juan Mata too.

Jose Mourinho almost repeated his famous run down the Old Trafford sideline in anger at that non decision, but it has sparked the hosts into life. Juan Mata lashes in a shot from range but Petr Cech extends himself to make a fine save.

Mark Lawrenson
Former Liverpool defender on BBC Radio 5 live

Monreal had his arm across the midrift of Valencia but Valencia has gone down so easily.

John Murray
BBC Radio 5 live commentator at Old Trafford

Valencia looked to have been taken down, he'd beaten Monreal round the outside.

Jose Mourinho is anything but stationary now! Antonio Valencia bursts into the box and goes down as Nacho Monreal reaches across him - nothing given!

Got to be a penalty. 

Image source, Getty Images

Phil McNulty
BBC Sport chief football writer at Old Trafford

This is now very tame stuff. Barely a chance since Alexis Sanchez's header and Old Trafford is very subdued - with good reason. Dull.

Few fruity chants still being aimed at Jose Mourinho from Arsenal's fans, probably to keep themselves occupied.

I thought Matteo Darmian was unlucky to be booked earlier but he's perhaps even luckier now to still be on the field. He catches Carl Jenkinson high and late and should get a second yellow. Referee Andre Marriner has let him off the hook there.

John Murray
BBC Radio 5 live commentator at Old Trafford

Jose Mourinho is standing on the sidelines stock still like one of those mannequins that are all the rage at the moment.

Image source, Reuters

Ander Herrera tries a devilishly difficult volley from a half-cleared corner, Paul Scholes at Villa Park stuff, but only succeeds in getting a sore instep and finds the eighth row up. Jose Mourinho looks slightly more grumpy than usual. 

This game is sliding downhill towards the precipice of a goalless first half now. Alexis Sanchez looks the most likely for the visitors but when he produces a picturebook pass over the top Aaron Ramsey's control can't match it.

Manchester United now win a corner...

Alexis Sanchez knows the game, and he loses Antonio Valencia with a delicious little turn to set Arsenal on their way. Unfortunately for him, Michael Carrick slides in to cut it out. 

Image source, Getty Images