Guardiola and City win battle of Manchester against old foes Mourinho and United
First half goals by Kevin de Bruyne and Kelechi Iheanacho put Pep Guardiola's side in total control as they dominated United for most of the first half by showing greater quality on the ball.
Zlatan Ibrahimovic handed Jose Mourinho's team a lifeline just before the break with a very well taken finish, but City held firm in the face of an aerial onslaught in the second-half to maintain their unbeaten start to the season.
Mourinho gave Jesse Lingard and Henrikh Mkhitaryan their first starts of the season, but both were replaced at half-time after failing to make an impression.
Marcus Rashford's second-half introduction sparked United into life, but they failed to capitalize on a shaky performance by City goalkeeper Claudio Bravo.
The Chilean’s addition to the team has seen England stopper Joe Hart allowed to leave the club for Italian team Torino, and Bravo has endured a torrid trolling on Twitter since. Nevertheless manager Guardiola said he was happy with his new man's efforts.
Bravo may not be great at catching crosses but he's good with his feet. #Bravohart— Gary Lineker (@GaryLineker) September 10, 2016
"Second half we knew they changed system and with these long balls they are much more strong than us," he said.
"With these long balls anything can happen, but Nico (Otamendi) in particular was fantastic.
"We played good. We won the ball back quickly and created a lot of chances, but when you have that many chances to counter attack against a team like Manchester United you have to take advantage.
"Claudio's performance was one of the best I've ever seen. He continued playing after a difficult first half.
"His personality means a lot - how you react after making a mistake is so important."
The defeat ended United's 100 percent start to the league campaign and Mourinho admitted after the game he made a mistake with team the wrong team.
"I think in the first half they were much better than us," said Mourinho.
"We start the game with lots of players below their normal level. You need to be sharp, the way you think, the way you play. We had a few players below that and we paid for it.
"The second half was much better. When they played Fernando after a couple of minutes it was because they felt what everyone else was feeling - that we were in control.
"Honestly, I had two or three players in the first half that I wouldn't have picked if I could look back at it. They didn't give me what I want. It's their fault, it's my fault."
In the day’s other football derby, Celtic played Rangers in the first Old Firm league clash for four years since Rangers’ promotion to the Scottish Premiership. A hat-trick from Moussa Dembele and goals from Scott Sinclair and Stuart Armstrong gave the hosts a 5-1 win at Celtic Park.
Meanwhile North of the border, Celtic are giving Rangers a real spanking.— Gary Lineker (@GaryLineker) September 10, 2016
Man Utd: De Gea, Valencia, Bailly, Blind, Shaw (Martial 81), Fellaini, Pogba, Mkhitaryan (Herrera 46), Rooney, Lingard (Rashford 46), Ibrahimovic.
Man City: Bravo, Sagna, Stones, Otamendi, Kolarov, Fernandinho, Silva, Sterling (Sane 60) De Bruyne (Zabaleta 90), Nolito, Iheanacho (Fernando 52).