Match ends, Manchester City 3, Manchester United 1.
Manchester United manager Jose Mourinho said Manchester City's preparations for their derby victory were helped by playing in two "friendly" matches during the past week.
City returned to the top of the Premier League as goals from David Silva, Sergio Aguero and Ilkay Gundogan earned the champions three points at Etihad Stadium.
But Mourinho said the hosts had an advantage as their past two games - home thrashings of Southampton and Shakhtar Donetsk in which they won by an aggregate 12-1 - were significantly more straightforward than his team's most recent matches.
This was United's third away game in succession, following back-to-back wins at Bournemouth last weekend and Juventus on Wednesday.
"It's a heavy result for the effort of a team that had three away matches in the same week, with a super difficult match of a high, demanding level in Juventus against a team that had two friendly matches at home against Southampton and Shakhtar," Mourinho told BBC Radio 5 live.
"The physical fatigue and the mental fatigue leads to mistakes. They were tired physically and mentally. You need to be in football or another high-level sport to know what that is. The concentration of the big matches, they dry you. You are dry inside. To be ready again for another big match is not easy."
City's victory was rarely in doubt after Silva bundled home an early goal to give them a narrow interval advantage.
They got the second their superiority deserved with Aguero's rasping, rising finish past David de Gea three minutes into the second half following an exchange of passes with Riyad Mahrez.
Mourinho's side, without injured Paul Pogba, barely mounted a serious threat but were given hope of earning an unlikely point just before the hour when Romelu Lukaku was hauled down by Ederson seconds after he had come on as substitute. Anthony Martial sent the Brazilian keeper the wrong way from the spot.
It briefly revived memories of last season's dramatic derby here when United came from two goals down to win, but City never looked like losing control and wrapped up the win two minutes from time when substitute Gundogan took advantage of static United defending to beat De Gea from close range following a 44-pass move.
"We deserved the victory," City manager Pep Guardiola told BBC Sport. "The first half we played a little bit with fear and we didn't want to lose the ball. We didn't want to attack and they defended well.
"In the second half the game was a bit open so we had to find more space and we made a good performance against a top, top team."
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Who can stop rampant Man City?
Manchester City's answer to Liverpool briefly returning to the head of the Premier League table earlier in the day was emphatic because this win was as comfortable as the scoreline suggests, arguably even more so.
Liverpool and Chelsea remain unbeaten in the Premier League, Jurgen Klopp's side beating Fulham 2-0 and Maurizio Sarri's side slipping as they were held to a 0-0 draw by Everton at Stamford Bridge.
They remain very much in the title shake-up, as do fourth-placed Tottenham.
The problem for the chasing pack appears to be that Manchester City are operating on a different level to everyone else.
United were probably feeling pleased with themselves that somehow, despite barely laying a glove on City, they were actually still in contention for a point until Gundogan's late goal ended all the arguments.
And it was a goal that summed up City under Guardiola.
The finish looked simple enough as Gundogan slipped in past some static United defenders to score with ease but it crowned a 44-pass sequence, the most before a goal since Juan Mata scored for Manchester United against Southampton in September 2015.
City are two points clear of Liverpool but have a goal difference of +31 as opposed to +18 and this was another of their most difficult fixtures negotiated with their usual flair.
Man City's old guard key to victory
Manchester City's latest win was built on the foundations of three established members of their recent glories.
Aguero may have gone from brunette to striking blonde but under the new hairstyle remained the same lethal striker who has been the centrepiece of so many of their successes.
It was classic Aguero when he scored City's crucial second three minutes after the break, exchanging passes with Mahrez before lashing home a near-post finish that carried so much power, De Gea barely had time to react.
It was his 151st goal in 218 Premier League games and his 208th goal in 307 games in all competitions for City. These statistics emphasise his status as one of the modern game's great strikers.
David Silva, at 32 now an elder statesman at City, set them on their way with the early opener and showed his usual knack of finding space in crowded areas and ability to dictate tempo even at the most frenetic times.
At the heart of it all was the unsung Fernandinho, the 33-year-old Brazilian patrolling midfield with class and quality, working effectively in the shadows.
Guardiola knows his worth - and will also know he will be very difficult to replace when the time comes.
Man United's slow start finishes title hopes
Mourinho has bemoaned his team's slow starts this season and appears at a loss to discover the cure. And it is now too late to salvage any title aspirations.
They had survived a couple of narrow escapes before Silva scored after 12 minutes to put them on the back foot once more and to give City the sort of control and impetus they relish.
United clearly missed the injured Pogba, who helped turn this derby around last season, but this was still a performance lacking in invention and serious attacking threat.
And while Gundogan's goal crowned a glorious move, Mourinho will have looked on in anguish as United defenders stood around like statues.
United are now 12 points adrift of City. They can forget the Premier League title for another season.
Man of the match - David Silva (Manchester City)
'Ours was a performance with mistakes' - what they said
Manchester City manager Pep Guardiola speaking to Match of the Day: "We wanted to play good in front of our fans and we know how important it is to play in this game. We did well [in the second half] and that goal from Sergio Aguero helped us a lot after half-time."
Manchester United boss Jose Mourinho to Sky Sports: "We were in the game until the 80th-something minute and the third goal killed the spirit and morale of the team.
"One thinking is a bad performance and one thinking is a performance with mistakes. I think ours was a performance with mistakes.
"We are outside the top four, how can we speak about the title? Let's fight to close the gap to jump into the top four. If we jump into the top four then let's see the difference."
A start to forget for United - the best of the stats
- It is the first time since 1990-91 that Manchester United have lost as many as four of their opening 12 games in a top-flight season.
- This is the first time since 1977-78 that United have a negative goal difference after 12 games of a top-flight season.
- It is the first time in English top-flight history that three clubs have remained unbeaten in their opening 12 games of the season (Manchester City, Liverpool and Chelsea).
- Only Fulham (0) have kept fewer clean sheets than Manchester United (1) in the Premier League this season.
- Man City's Sergio Aguero has scored eight Premier League goals against Manchester United - only Alan Shearer (10) has more against the Red Devils in the competition.
- There were just 30 seconds between Lukaku coming on as a substitute for Man Utd, and winning the penalty that made it 2-1.
- David Silva has scored in three consecutive home games in all competitions for Man City for the first time.
- This was Jose Mourinho's 300th Premier League game as manager - despite defeat today, he's won more games than any other manager in their first 300 in the competition (189).
Manchester City travel to West Ham on Saturday, 24 November (15:00 GMT) in the Premier League, while Manchester United host Crystal Palace on the same day (also 15:00).
- 20Bernardo SilvaBooked at 33mins
- 21SilvaSubstituted forFodenat 90+2'minutes
- 26MahrezSubstituted forSanéat 62'minutes
- 10AgüeroSubstituted forGündoganat 75'minutes
- 33Gabriel Jesus
- 1De Gea
- 23ShawBooked at 42mins
- 21HerreraSubstituted forMataat 73'minutes
- 14LingardSubstituted forLukakuat 57'minutes
- 10RashfordSubstituted forSánchezat 73'minutes
- Anthony Taylor
- Shots on Target
Second Half ends, Manchester City 3, Manchester United 1.
Corner, Manchester City. Conceded by Alexis Sánchez.
Substitution, Manchester City. Phil Foden replaces David Silva.
Foul by Benjamin Mendy (Manchester City).
Alexis Sánchez (Manchester United) wins a free kick in the defensive half.
Goal! Manchester City 3, Manchester United 1. Ilkay Gündogan (Manchester City) left footed shot from very close range to the centre of the goal. Assisted by Bernardo Silva with a cross.
Attempt blocked. Juan Mata (Manchester United) right footed shot from the left side of the box is blocked. Assisted by Nemanja Matic.
Attempt missed. Ilkay Gündogan (Manchester City) right footed shot from outside the box misses to the right. Assisted by Raheem Sterling.
Benjamin Mendy (Manchester City) wins a free kick in the defensive half.
Foul by Alexis Sánchez (Manchester United).
Substitution, Manchester City. Ilkay Gündogan replaces Sergio Agüero.
Attempt missed. Leroy Sané (Manchester City) left footed shot from outside the box is high and wide to the left. Assisted by Raheem Sterling following a fast break.
Attempt blocked. Nemanja Matic (Manchester United) right footed shot from the centre of the box is blocked.
Foul by Benjamin Mendy (Manchester City).
Alexis Sánchez (Manchester United) wins a free kick on the right wing.
Substitution, Manchester United. Alexis Sánchez replaces Marcus Rashford.
Substitution, Manchester United. Juan Mata replaces Ander Herrera.
Fernandinho (Manchester City) wins a free kick in the attacking half.
Foul by Marouane Fellaini (Manchester United).