Having survived a strong opening from Roy Hodgson's on-song Baggies, United took control of an entertaining game midway through the first period and rarely looked like slipping up after Rooney diverted home Chicharito's shot.
The England striker then clinically converted a penalty after the lively Ashley Young had been felled, by which point Jonas Olsson had been sent off for garnering two yellow cards. United's victory took on added significance when news filtered through that Manchester City had lost at Swansea City.
Sir Alex Ferguson had publicly pondered his team selection after Thursday's Europa League defeat to Athletic Club, with next week's decisive trip to Bilbao looming large. United's focus on domestic matters became apparent with the returning experience of Rio Ferdinand, Michael Carrick and Paul Scholes,while Danny Welbeck's inclusion on the right flank hinted at the hosts' attacking intent.
It was the visitors, however, who forged the game's first opening of note. After James Morrison pinched possession midway inside the United half, Liam Ridgewell curled a fine cross into the hosts' six-yard box, where the onrushing Keith Andrews could only steer the ball wide of De Gea's goal.
Only a terrific block from Evans prevented Marc-Antoine Fortune from unleashing a shot deep inside the hosts' area, while Morrison blazed the rebound comfortably over the bar. United's first attempt came from Ashley Young after a weaving run from Welbeck, but the winger's shot was batted away by ex-Red Ben Foster.