Wayne Rooney broke the deadlock on the stroke of halftime with a close-range shot, however; his slip-up enabled the hosts to restore parity one minute from the hour mark.
The England international's awkward pass was intercepted and eventually Hull were awarded a penalty-kick which Craig Fagan converted to cancel out the Red Devils' slender lead.
But later on, Rooney atoned for his mistake to set up two more goals and give United a vital win.
He whipped in a cross that was accidently diverted into the net by Hull defender Andy Dawson on 73 minutes.
Eight minutes from time, Rooney flicked the ball to Dimitar Berbatov, whose point-blank clinical finish was unstoppable.
Now United are in second place with 40 points, two adrift of Chelsea who won only one league game out of their last five.