Danny Welbeck scored the winning goal against his former club as Arsenal beat Manchester United 2-1 to reach the semi-finals of the FA Cup.

The England international struck in the second half, after Wayne Rooney had cancelled out Nacho Monreal's strike before the break, to seal a first win at Old Trafford since 2006 for the Gunners.

The visitors started brightly and Alexis Sanchez caused a moment of early panic inside the United box with a strike that was blocked by Chris Smalling.

Louis van Gaal's side gradually began to take control of the match, with Arsenal sitting deep and allowing their opponents time on the ball.

For all of United's possession, it took them 20 minutes to register their first shot on goal, but after being found in space inside the box, Ashley Young blazed his attempt high over the bar.

However, in the 25th minute Arsenal took the lead, as Alex Oxlade-Chamberlain danced past couple of challenges on the edge of the box, before sliding in Monreal to place a composed finish past David de Gea.

United responded well to that setback and within four minutes they had levelled the scores when Angel Di Maria's deep cross was headed in by Rooney.

The game was being played at a frenetic pace and the Gunners felt that they should have had a penalty when Welbeck appeared to be dragged down inside the box by Marcos Rojo, but the referee waved away their appeals.

Welbeck was involved again moments later, as he rose highest to meet an Oxlade-Chamberlain cross, before seeing his header saved by De Gea.

As the game approached half time, United almost snatched the lead, but Wojciech Szczesny was alert to keep out Di Maria's near-post effort.

Santi Cazorla then saw a free kick saved, while Marouane Fellaini was also denied, as the two teams headed into the break on level terms.

After the break, the Gunners were the first to threaten when Cazorla found Sanchez in space, but the Chilean's attempt deflected kindly into the gloves of De Gea.

A number of stoppages disrupted the flow of the game, but Di Maria had a sight of goal for the hosts when he latched on to Fellaini's pass and dragged a shot wide of the far post.

Within minutes, Arsenal had regained their lead and it was former United player Welbeck who scored on his return to Old Trafford.

The striker was quick to latch on to a poor back-pass from Antonio Valencia and he took the ball past De Gea, before slotting into the unguarded net.

Once again the hosts came close to a quick equaliser, but following a corner Smalling could only send the ball over the bar.

Arsenal continued to look a threat on the counter and they nearly grabbed a third goal when Cazorla met Sanchez's cross on the volley, but his strike was kept out by De Gea.

United's hopes of getting back into the game suffered a blow as Di Maria was sent off for grabbing the shirt of referee Michael Oliver, just moments after he had been booked for diving.

Arsenal then took control of the match and they were inches away from grabbing a third in stoppage time when Sanchez's strike was tipped wide of the post by De Gea.

It would prove to be the final chance of the evening, as Arsenal held on to book their place in the last four of the cup and maintain their defence of the trophy.