Rooney took just eight minutes to beat Hull goalkeeper Boaz Myhill, latching onto the rebound after a shot from Paul Scholes was parried. But it proved tough for United until Rooney added three more in the last ten minutes to take his tally for the season to 20 goals.
"He is in great goalscoring form right now," United manager Alex Ferguson said. "We are happy, being top is significant at this stage of the season. I know Chelsea have got games in hand but they have to win those games."
United has a two point lead over both Arsenal and Chelsea. Arsenal, though, has a game in hand over United and Chelsea has played two fewer matches than the champions. United and Hull were playing on FA Cup fourth-round day after being eliminated from the competition earlier this month.
Ferguson used his program notes to urge fans to unite despite their concerns about the club's debts, but the match started with chants against the owning Glazer family. United, though, profited early on from Myhill's failure to hold onto Scholes' shot and Rooney pounced on the loose ball.
With Michael Owen making a rare start, United struggled to find a second goal until Dimitar Berbatov replaced the English striker with 17 minutes left. Rooney then exploited a chaotic situation in the area in the 82nd to make it 2-0 after Myhill fumbled Nani's free kick onto his own bar and then flattened defender Andy Dawson.
The England forward then headed in Nani's cross four minutes later and added the fourth in stoppage time when he slotted home from Berbatov's cross.