Trebles in Saturday's 5-0 thrashing of Bolton Wanderers and the 8-2 hammering of Arsenal a fortnight ago have given the England forward a tally of eight league goals after four games and he has scored in every match.
It is a far cry from the wretched time he was enduring a year ago when off-field scandals, including the saga of whether he would stay at the club, and the loss of his scoring touch led to some critics questioning whether he was past his best.
Rooney now looks a different player - not just because of his well-documented hair transplant - and has put his return to form down to having a break after last season.
"I had a long time to rest and I had a very good pre-season, I stayed clear of injuries and it's obviously helped me for the start of this season," he told ESPN television.
Already closing in on the 11 league goals he managed last season, Rooney is showing the type of sharpness he had in the 2009/10 campaign when he scored 34 goals in all competitions.
He has notched seven hat-tricks since joining United from Everton in 2004, the total number achieved by the great Bobby Charlton although still some way short of Denis Law's club record 18.
"It's a fantastic achievement considering he's only 25 and he's got many years in front of him," United manager Sir Alex Ferguson said.
Rooney's only hat-trick last season, which was completed in 14 minutes against West Ham United, was marred by a foul-mouthed tirade to a television camera that earned him a two-match ban.
This season there have been only smiles, shared by his team-mates who are revelling in Rooney's good form, the beginnings of which started towards the end of last season when his partnership with Javier Hernandez blossomed.
The Mexico striker, who scored twice against Bolton on his first start this season after suffering concussion on the pre-season tour of the United States, said playing alongside Rooney brought out the best in others.
"We all know he is a world class player," said Hernandez.
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