Wellback scores against ManU

England striker Welbeck joined Arsenal from United in a £16m deal on deadline day in September - and came back to score the goal that gave the Gunners their first win at Old Trafford since 2006.

It ensures Louis van Gaal, the manager who sanctioned his sale, will almost certainly end his first season empty-handed.

Nacho Monreal gave Arsenal a first-half lead but Wayne Rooney equalised with a flying header from Angel Di Maria's cross - the high point of the Argentine's night as he was later dismissed for two yellow cards after Welbeck had restored Arsenal's advantage.

And on a great night for manager Arsene Wenger after United had won 11 of the last 15 meetings between the sides in all competitions, Arsenal are now huge favourites to reach another FA Cup final after drawing either Reading or Bradford City in the semi-final.

The hero of the night, however, was Welbeck as he punished United, the club where he scored 29 goals in 142 appearances before switching to Arsenal after Van Gaal brought in Radamel Falcao.

Falcao was not even called from the bench amid United's increasing panic, which saw the great tactician Van Gaal end with the giant figures of Marouane Fellaini and Chris Smalling up front.

United have sailed close to the wind on many occasions on the back of average performances this season, digging out victories without looking convincing.

There was no reprieve here, though, and now a place in the Premier League's top four and a return to the Champions League is their sole aim for the rest of the campaign.

For Arsenal, this was a demonstration of the sort of resilience that saw them win at champions Manchester City this season and now end that recent curse here at Old Trafford.

And in a season when so much criticism has been aimed at referees, praise must be reserved for a magnificent performance by Michael Oliver, who remained calm and got the big decisions right in an increasingly frantic Old Trafford environment.

Old Trafford has been the scene of many low-key games this season - but there was a big-match atmosphere around the stadium as United and Arsenal produced a first 45 minutes to savour.

Arsenal's crisp passing had already caused United problems before they took the lead in the 25th minute. Alex Oxlade-Chamberlain was the creator with a weaving run along the edge of the area before finding Monreal, who beat David De Gea at the near post with composure.

The lead lasted only four minutes, United replying with quality of their own as Di Maria's perfect delivery dropped between Arsenal's defenders to be met by the flying figure of Rooney, who directed a powerful header beyond Wojciech Szczesny.

Di Maria was looking much more comfortable, as well as dangerous, on the flank and he stole in behind Arsenal to get in a low effort that Szczesny blocked with his legs at the near post.

Van Gaal made a double change at the interval, sending on Phil Jones and Michael Carrick for Ander Herrera and Luke Shaw - but there was no instant cure for the uncertainty that had plagued United's defence.

And it was in evidence again as Arsenal went back in front just after the hour. Antonio Valencia's backpass sold De Gea short and Welbeck reacted quickly to nudge the loose ball around the keeper and roll it into the unguarded net.

Welbeck received warm applause from large sections of United's support when he was replaced by Olivier Giroud. There were some jeers mixed in but he clearly remains a popular figure at Old Trafford.

Seconds after that switch De Gea produced a miraculous piece of goalkeeping to keep United in contention, somehow clawing out Santi Cazorla's shot from Alexis Sanchez's cross.

United's play, as well as the noise from their supporters, carried an air of desperation and their cause was not helped by a moment of madness from Di Maria that saw him sent off with 13 minutes left.

After being booked for diving, the frustrated Argentine then tugged at referee Oliver's shirt as he walked away, with inevitable consequences.

It was one of many lows on a night when the frustrations of United and their supporters bubbled to the surface - and their trophy hopes ended
.