Man Utd 4-1 Middlesbrough
United went ahead on three minutes when Nani drove in a cracking shot from 30 yards but Jeremie Aliadiere soon equalised with a precise header.
Nani robbed Stuart Downing and played in Rooney, to smash United's second.
After the break Carlos Tevez slotted in after a sublime Rooney back-heel and he added a fourth with a deflected shot.
United scored four goals in a fourth successive game - the first time in 100 years they have done so.