Wayne Rooney matched his three-goal performance against Arsenal before the international break in United's 5-0 rout of Bolton.
The emphatic victory kept the champions on top based on goal difference ahead of City, which had earlier beaten Wigan 3-0 with Sergio Aguero handling the scoring.
"We've concentrated on ourselves," Rooney said. "We knew it was going to be a difficult game, we focused, made sure we got the win and thankfully the win was a bit easier than we thought."
The only other unbeaten team is fourth-place Stoke, which handed Liverpool its first loss of the season as Jon Walters' penalty kick secured a 1-0 win.
The north London rivals finally celebrated their first wins: Arsenal capitalized on Swansea's goalkeeping miscue to beat Swansea 1-0 and former Gunners striker Emmanuel Adebayor scored on his Tottenham debut in a 2-0 win at Wolverhampton Wanderers.
Also on Saturday, Daniel Sturridge clinched third-place Chelsea's 2-1 win at Sunderland while Everton was held 2-2 at home by Aston Villa.
It is United, though, that's leading the way as Sir Alex Ferguson's side looks to extend the English title record to 20.
After an 8-2 thrashing of Arsenal two weeks ago, Javier Hernandez opened the scoring after just four minutes from Nani's cross.
On his first start of the season, the Mexico forward made it 4-0 in the 58th, turning in the ball at the far post after Michael Carrick's shot was blocked.
But Rooney stole the show with his first two goals coming between Hernandez's, with defender Phil Jones creating both.
Midway through the second half, the England striker curled in his 10th goal in his last six appearances for club and country.
"It was excellent, the movement and pace they play at was just fantastic," Ferguson said of the Rooney-Hernandez partnership.
Despite another crisp display of attacking interplay from Man City, manager Roberto Mancini was not satisfied.
"We had 15 chances in the first half and we scored only one goal — this is a problem because the game can change any moment," Mancini said. "We have started the season very well but the season will be long.
"If we want to arrive at the end of the season still at the top we need to improve."
Aguero, though, has five goals in two home games for City since arriving from Atletico Madrid.
Carlos Tevez, making his first start of the season, had a hand in Aguero's early opener before then missing a 19th-minute penalty.
Tevez was replaced by Nasri and the France midfielder finally unlocked the Wigan defence again in the 63rd minute, nudging a backheel from David Silva into Aguero's path to curl a shot low into the corner.
Aguero scored his third goal six minutes later, again assisted by Silva, who spun off his markers and delivered a defence-splitting throughball for the striker.
No team was under more pressure to win Saturday than Arsenal, which had been in a state of despondency for two weeks since the United collapse left the team with one point from three matches.
But Andrei Arshavin's goal five minutes before halftime proved to be enough for the victory.
After collecting the ball, Swansea goalkeeper Michael Vorm tried to quickly clear it but his underhanded throw from the right of the penalty area deflected off Angel Rangel's heel.
And the loose ball fell to Arshavin, who scored from a tight angle.
At Stoke, Liverpool struggled with the hosts' physical approach, and after Jamie Carragher fouled Walters in the box, the Stoke striker fired a penalty past Jose Reina.
Chelsea's gamble of dropping misfiring striker Fernando Torres paid off, with a back-heeled goal from his replacement, Sturridge at the start of the second half after John Terry's first-half strike.
South Korea forward Ji Dong-won scored in stoppage time.
Tottenham, which lost its opening two matches, has brought in Adebayor on loan from City.
The Togo striker scored midway through the second half at Wolves after collecting a pass from fellow Tottenham newcomer Scott Parker. Jermain Double scored the second after a nice passing play with Niko Kranjcar.
At Goodison Park, Stiliyan Petrov and Gabriel Agbonlahor scored as Aston Villa twice came from behind to tie Everton and preserve its unbeaten start.
Leon Osman and Leighton Baines scored for Everton.