Manchester City's defeat at Tottenham at lunchtime opened the door for United to move to the summit and they grasped the opportunity, winning 3-0 at Old Trafford.
After an admirably stubborn effort in the opening stages, Sunderland buckled in first-half injury time when Memphis Depay scored his first Premier League goal.
Rooney bundled home Anthony Martial's cross to end a barren run in the Premier League that had stretched to 999 minutes, before Juan Mata added a third at the death
Louis van Gaal has had his doubters during his 14-month spell in charge, but United are now top of the table for the first time since they beat Swansea 4-1 in David Moyes' first game in charge on August 18 2013.
United's stay at the top of the pile then, just like Moyes' tenure, was a brief one - they were knocked off the top the following day - but Van Gaal will be hoping his team can remain there for the rest of the season.
Van Gaal's old friend Dick Advocaat can only dream of climbing so high in the standings
Sunderland are bottom of the table after seven matches.
Advocaat made his intentions clear from the start
Ola Toivonen came in for Jermain Defoe and Sunderland lined up in a defensive 4-5-1 formation.
As has been the case for the majority of the season, United had plenty of possession but initially struggled to do anything with it.
Matteo Darmian and Antonio Valencia bombed on down the left and right flanks respectively while Martial's trickery and strength caused the visitors problems, but Sunderland goalkeeper Costel Pantilimon saw little of the ball.
The only time Sunderland came under any real threat was when Pantilimon booted the ball up in the air and caught it outside the penalty area.
Luckily for the goalkeeper, he was spared a card and Mata drove the free-kick into the wall.
John O'Shea headed into David de Gea's arms and the Spaniard then saved with his legs from Yann M'Vila during a rare promising spell for the visitors.
The home fans became anxious as Mata, Rooney, Martial and Michael Carrick were guilty of wasteful passing in the final third.
But there was no need to worry
In the fourth minute of first-half injury time Daley Blind found Mata, who squared to Depay and he finished from close range.
Sunderland brought on Steven Fletcher for Adam Johnson, but 38 seconds into the second half they conceded again.
Martial bundled his way into the box and squared for Rooney
Lee Cattermole tried pushing the United captain out of the way, but the ball struck the striker's knee and went in.
The strike meant Rooney became United's joint third-highest league goalscorer, moving alongside Denis Law.
De Gea saved at his near post from Toivonen and Patrick van Aanholt, but Sunderland never looked like getting back into the game.
Depay wasted a chance for a third, but Mata fared better, driving home Ashley Young's cross in the final minute to spark chants of "We are top of the league" from the Stretford End.
TWEET OF THE MATCH
"Back at the top where we belong ? positive performances at @ManUtd today!"
Andrew Cole, @vancole9
https://twitter.com/vancole9/status/647802380491321344
PLAYER RATINGS:
Manchester United:
David de Gea: 7
Antonio Valencia: 6
Chris Smalling: 6
Daley Blind: 7
Matteo Darmian: 6
Michael Carrick: 6
Morgan Schneiderlin: 6
Juan Mata: 8
Wayne Rooney: 7
Memphis Depay: 8
Anthony Martial: 8
Subs:
Bastian Schweinsteiger: 6
Phil Jones: 6
Ashley Young: 7
Sunderland
Costel Pantilimon: 7
Billy Jones: 6
Younes Kaboul: 6
John O'Shea: 5
Patrick van Aanholt: 6
Lee Cattermole: 5
Yann M'Vila: 7
Jeremain Lens: 6
Ola Toivonen: 6
Adam Johnson: 5
Fabio Borini: 5
Subs:
Steven Fletcher: 5
Sebastian Larsson: 5
STAR PLAYER
Juan Mata: Seen as one of the players in jeopardy following the arrivals of Anthony Martial and Memphis Depay, but the Spaniard has risen to the challenge fantastically
He set up Memphis Depay with the slightest of touches in the box and added a deserved goal of his own in the final minute.
MOMENT OF THE MATCH
Memphis Depay's goal: Van Gaal was criticised for playing Daley Blind in defence earlier this season, but the Dutchman has taken to the role well
Just as he did against Ipswich in midweek, he strode out with the ball and pinged a delightful ball to Mata, who squared to Depay and he did the rest from close range
It was a wonderful goal that had everyone inside Old Trafford on their feet.
VIEW FROM THE BENCH
Dick Advocaat sensed he would have little joy attacking United, so he went for a defensive 4-5-1 formation
Sunderland stood off Michael Carrick and Morgan Schneiderlin, allowing them to probe Sunderland's back line from distance, which they did well
Advocaat's decision to leave Jermain Defoe on the bench for the whole match was baffling
Louis van Gaal's decision to field two holding midfielders looked to be unwise, but Carrick and Schneiderlin had a big influence on the game
His decision to allow Anthony Martial to lead the line was clever
Younes Kaboul and John O'Shea had no answer to the teenager's strength or pace.
MOAN OF THE MATCH
Sunderland's lack of fight and ambition: The Black Cats showed little imagination or invention on the attack
More often than not they had nine men in their own half
Not a great message to send to the thousands of supporters who had trekked across from the north-east to Old Trafford and it does not bode well for their title chances.
WHO'S UP NEXT
Manchester United v Wolfsburg (Champions League, September 30)
Sunderland v West Ham (Premier League, October 3)
Source : PA
Source: PA