Ramires stretched to force a wonderful, improbable stop from De Gea with Daniel Sturridge waiting behind for a simple tap-in.
The Reds no.1 gathered the resulting corner at the second attempt and also kept out an unmarked Sturridge while Torres sent an unconvincing overhead kick wide as Chelsea had few problems creating chances. But Nani showed them how to finish with a piece of individual magic, collecting Jonny Evans' diagonal pass, advancing on goal and fizzing a firecracker of a finish past Petr Cech's flailing right hand.
With a two-goal advantage, United continued to look menacing and, just before half-time, Rooney was involved early on in a move that saw Phil Jones maraud forward from centre-back. Eventually, John Terry's clearance bounced fortuitously off Nani and into Rooney's path. He calmly despatched a third.
This was never going to be a cakewalk for the champions and substitute Nicolas Anelka made an immediate impact at the start of the second half when setting up Torres for a clever finish over De Gea. Mata forced the Reds stopper into action again but United should have extended the lead when Nani broke onto a Rooney pass and, after seeing his shot come back off the bar, was fouled by Jose Bosingwa as he latched onto the rebound.
Phil Dowd opted against carding the Portuguese defender and no punishment was meted out as Rooney slipped when taking the spot-kick, evoking