Quick-fire goals from Ji-Sung Park and Cristiano Ronaldo effectively killed off Arsenal's hopes of staging a fightback on home soil after trailing 1-0 from last week's first leg at Old Trafford.
Ronaldo claimed his second and United's third of the night on the hour mark, but a perfect night for the Red Devils was soured by the 75th minute dismissal of Darren Fletcher.
Before the match, Gunners boss Arsene Wenger spoke of his belief that his youthful side could bounce back from their first-leg deficit.
However, he sat bemused on the bench as his side conspired to give away two goals from which they would never recover.
All the pre-match optimism around the Emirates Stadium was undone when Kieran Gibbs slipped and allowed a hopeful Ronaldo cut-back to reach the surprised Park.
The busy Korean took a touch before finding the back of the net from eight yards with a dinked finish over the diving Manuel Almunia.
The Spanish keeper was then to blame for the killer second goal which left Arsenal needing to score at least three times on the night.
Ronaldo won a cheap free-kick following a tussle with Robin van Persie 40 yards from goal.
The Portuguese star then brushed himself off before firing in the long-range free-kick which beat Almunia to his left.
The free-kick was rapier-like, but Almunia was slow to react and should have got his hands to the ball and pushed it away.
The keeper slightly redeemed himself after 20 minutes when he clawed a curling effort from the hard-working Wayne Rooney behind for a corner.
United were dominant at this stage and Ronaldo should have capitalised when he was left unmarked at a corner moments later only to glance an eight-yard header wide of the mark.
The second half was a similar tale as, although Arsenal had top scorer Robin van Persie back from injury alongside Emmanuel Adebayor in attack, they could not gain a foothold in the game.
And missing several key personnel in defence, they were always likely to be hit on the break when they had to chase the game.
United were happy to sit back and soak up the pressure with Fletcher, Anderson and Michael Carrick providing an impenetrable shield in front of the defence.
They were also always dangerous on the break and Almunia had to be at his best to tip away a Ronaldo shot from the edge of the penalty area after 55 minutes.
The warning was there for Arsenal though and a superb counter-attack resulted in United's third on the night.
Park and Rooney carved open an already stretched defence with a swift move and when the latter squared the ball to Ronaldo, the Portuguese winger found the back of the net with a sliding finish from the edge of the penalty area.
Sir Alex Ferguson then had the luxury of taking off Rooney and Patrice Evra, who were both just one booking away from missing the final through suspension.
However, the United boss could do little to protect Fletcher when he slid in to knock the ball away from Cesc Fabregas with a superbly-timed tackle only for the referee to award a penalty.
United's bemusement then turned to dismay when Fletcher was shown a straight red card to rule him out of the final.
Van Persie converted the spot-kick high to Edwin van der Sar's left, but by then the game was over and United's dream of becoming the first team to successfully defend the Champions League trophy remains alive.