Goals from Nani, Wayne Rooney and Ji-Sung Park were enough to see off the home side, whose limp reply came from a deflected Thomas Vermaelen shot when the game was, to all intents and purposes, already over.
The first real chance fell to Andrey Arshavin after a delightful ball over the top of the Manchester United defence for the Russian to run on to on the left flank.
The diminutive attacker cut inside to try and curl a shot into the far post. The effort went wide and Samir Nasri, who was unmarked on the penalty spot, was furious.
United, playing with Rooney on his own in attack were nonetheless a clearly potent force. Gael Clichy was struggling on the right side again Nani and the Portuguese winger beat the Gunners left back twice within a matter of seconds in the seventh minute to deliver two dangerous crosses into the box.
The first required a toe-poke from William Gallas to get the ball away from Rooney and the second somehow eluded a crowd of players before eventually being hacked away by Denilson.
Nani nearly punished the Gunners, but put a shot just wide of the right post under pressure from two defenders, before getting his reward in the 33rd minute.
He skinned Clichy and Denilson on the right flank and lifted a ball into the area. A back-pedalling Manuel Almunia reached back and turned the ball into his own net for United to take a 1-0 lead.
Arsene Wenger's side were all over the place for United's second two minutes later. From defending an Arsenal attack, a loose pass set the visitors on a swift counter-attack with Rooney sneaking in to run on the a ball from Nani to fire a first-time low drive into the bottom left corner.
Nani had the chance to kill the home side off in the 40th minute when teed up to shoot on the edge of the area, but he pulled his right-foot shot wide of the left post.
Manchester United came out first after the interval looking calm and confident and made it 3-0 with another breakaway goal.
Ji-Sung Park raced away from his own half to latch on to a lofted ball from Paul Scholes. The Korean kept his cool, accelerated into the box and passed the ball into the net beyond Almunia.
Theo Walcott was brought on for a poor Denilson in the 60th minute, before Nicklas Bendtner and Emmanuel Eboue entered the fray.
A slip by the latter in the 75th minute almost gave Rooney another goal, but the United striker's shot went wide.
The Gunners did pull one back in the 80th minute through an acrobatic effort from Vermaelen, whose shot from the edge of the area was deflected off Johnny Evans past Edwin Van der Sar.
With the clock ticking down to full-time, Gallas had a free header with his back to goal, but directed the ball well wide from three yards out and the final whistle blew shortly afterwards.