It is likely to increase speculation about Pellegrini’s position at the Etihad Stadium, a year after he led City to a league and League Cup double, and he was at a loss to explain his side’s shortcomings.

Before the game Pellegrini had already delivered a damning verdict on his club’s season, saying they had thrown their campaign “into the garbage”.

“I don’t understand why a team only plays so well in the first 20 minutes,” the Chilean said at Old Trafford.

“We dominated, created chances, we had the ball. At 1-1, United started growing and their third goal gave them the confidence they did not have before.

“It is not just one problem. The same team played well for 20 minutes. Maybe it’s a lack of class at this moment. I don’t know.”

Asked if he was worried about his future at City, he replied: “I’m not talking about my position.”

City were bidding to record a fifth consecutive Premier League victory over their derby rivals and they made an ideal start when Sergio Aguero tapped in David Silva’s eighth-minute cross in front of the Stretford End.

But goals from Ashley Young and Marouane Fellaini saw United go in 2-1 up at half-time and further efforts from Juan Mata and Chris Smalling swelled the hosts’ lead before Aguero hit back at the death with his 100th City goal.

United have now won six league games in succession – including convincing wins over Tottenham Hotspur, Liverpool and now City – and will approach Chelsea’s visit next weekend brimming with new-found confidence.

“It’s three points. We are four points ahead of fourth in the table and I am very happy for the fans,” cheered United manager Louis van Gaal.

“You are playing for the fans and at the beginning of the season it was not so fantastic to be a United fan, because we have started 11 matches with 13 points and still they have supported us.

“I have seen what it means for them. They always support us when the results were not good. It’s the best atmosphere I have seen here. A fantastic result.”

And now, this week especially, they can go on the streets, hat up, and  say, ’We are this year the better team, because goal average is in our favour (over the two derby games).’”

United finished the game with 10 men after Michael Carrick was forced off  by injury, Van Gaal having already made his three permitted substitutions, and  the Dutchman admitted he had made a miscalculation.

“I must bring Michael Carrick off the pitch with an injury, which was a bit stupid from me as some players didn’t know we only had 10 men,” he said. “That was not so smart!”