Rooney, who scored a treble in the 8-2 demolition of Arsenal, scored twice before the break to set Sir Alex Ferguson?s side on the way to eclipsing the efforts of closest rivals City, who had beaten Wigan 3-0 earlier in the day.
The England striker scored his third in the second half as his efforts, along with a brace from Javier Hernandez, mean United have scored 18 times in their four opening league games.
Both Manchester clubs have signalled that this year?s duel for the title will be a two-horse race, but it is United who lead the way at this early stage on goal difference.
It was an afternoon where the old guard shone alongside a new generation of stars as Rooney combined brilliantly with Hernandez and summer signing Phil Jones.
Ferguson fielded an arguably stronger line-up than the one that hammered Arsenal at Old Trafford in their last match before the international break.
Mexican Hernandez returned to partner Rooney in place of Danny Welbeck, while Rio Ferdinand replaced Chris Smalling in the centre of defence.
The architect of this latest victory, perhaps even more so than Rooney, was Nani. His hat-trick of assists, and two more from the impressive Jones, was as much a part of this triumph as the fine finishing of Rooney and Hernandez.
The champions began the game at break-neck speed and Ferguson was left cursing referee Andre Marriner for not booking Kevin Davies after his challenge forced the United boss to replace Tom Cleverley with Michael Carrick.
The Bolton skipper escaped with a talking to and the angry United manager had only just caught up with play when his side took a fifth-minute lead.
Wayne Rooney found Nani on the right and the Portuguese crossed into the six-yard box where Harnandez arrived and beat Jussi Jaaskelainen at the near post.
United were immediately forced into the change when Cleverley limped off, and they also found themselves on the back foot in their own box.
The ball was cleared by Jonny Evans and fell to Chris Eagles, whose shot was cleared by Rooney when an equaliser looked odds-on.
Davies finally found his way into Marriner?s notebook when his tackle on Patrice Evra earned him a yellow card. Within seven minutes, United were further ahead.
Phil Jones exchanged passes with Nani after a throw-in and Rooney finished the cross after reaching the ball ahead of Gary Cahill and Dedryck Boyata.
Then in the 25th minute, United made it three. Former Blackburn midfielder Jones was involved again as he raced through home defence unchallenged.
He evaded Zat Knight?s attempted block before seeing his shot saved by Jaaskelainen?s legs. But Rooney was on hand to tap in the rebound. Hernandez thought he had added a fourth, only to see it ruled out by the referee?s assistant for offside.
He did, however, make it four in the 59th minute following good work from Nani. The winger weaved into the box and teed up Carrick, and the former Spurs midfielder saw his shot blocked and run loose into the path of the Mexican, who pounced once again.
Nine minutes later, the job was complete when Rooney completed his hat-trick with a right-footed strike after more creative magic by Nani.
United also missed countless chances to get closer to the eight goals put past Arsenal in their last outing, with Hernandez guilty of misfiring at least twice.
Source: AFP
Source: AFP