Manchester Utd 1 Arsenal 2

Danny Welbeck snatched the winner on his return to Old Trafford as FA Cup holders Arsenal booked their place in the last four.

Left-back Nacho Monreal put the visitors ahead midway through the first half with the second goal of his Gunners career, only for Wayne Rooney to head the equaliser straight away.

But Welbeck, who left United to join Arsenal last August, pounced on a defensive slip to take the Gunners to another Wembley semi-final, while his former club finished with 10 men after Angel di Maria was dismissed late on.

Arsenal reverted to the tactics that served them so well on their last trip to Manchester, dropping deep and waiting for opportunities on the counter-attack to surface as the game progressed.

Apart from an early Alexis Sanchez effort that struck Chris Smalling and rebounded to David de Gea, few did – and that applied to the home side as well in the opening quarter of the game.

Marouane Fellaini inexplicably hesitated when Smalling played him in, while Ashley Young might have done better after Fellaini chested the ball down to him, but speared his shot well wide.

And the visitors broke the deadlock on 25 minutes when the flashing feet of Alex Oxlade-Chamberlain bamboozled United’s defence as he skipped along the edge of the penalty area and found Monreal, who coolly clipped his finish past De Gea.

The lead lasted just three minutes as Di Maria supplied a tantalising left-cross for Rooney, who stole between the two Arsenal centre-backs and directed his header into the net.

With the game opening up, there were chances for both sides to take the lead before half-time, with Di Maria and Fellaini denied by Wojciech Szczesny and De Gea diving to hold Santi Cazorla’s free-kick.

But the start of the second half proved to be somewhat disjointed, with both sides forced to make early substitutions and struggling to adjust to those changes.

Cazorla robbed Smalling to set up a chance for Sanchez, which deflected through to De Gea – but another defensive lapse cost United dearly just after the hour mark.

Phil Jones and Antonio Valencia made a hash of collecting a long punt and the latter’s back-pass fell short of De Gea as Welbeck nipped in to take the ball around the keeper and score.

United came close to another immediate response, as Smalling bundled over the bar from a corner but, at the other end, De Gea kept his side in the tie, flinging out an arm to push away Cazorla’s left-foot volley.

However, the Red Devils’ hopes received a fatal blow 14 minutes from time when Di Maria was booked for a foul on Monreal and reacted by grabbing the shirt of referee Michael Oliver, earning himself a second yellow card.

De Gea denied Sanchez late on and, despite their numerical disadvantage, United kept up the pressure – but Arsenal held their nerve to seal a first win at Old Trafford since 2006.

Arsenal: Szczesny; Bellerin (Chambers 66), Mertesacker, Koscielny, Monreal; Cazorla, Coquelin; Oxlade-Chamberlain (Ramsey 51), Ozil, Sanchez; Welbeck (Giroud 74).