Ole Gunnar Solskjaer blasted his “sloppy” players and admitted the “magic” was missing as Oliver Burke fired rock bottom Sheffield United to a stunning win.
Skipper Harry Maguire had hauled United level after as former City youth skipper Kean Bryan opened the scoring for the Blades in the first half.
Solskjaer said: “When you concede two bad goals it will be difficult.
“We didn’t create enough and didn’t penetrate in behind to score enough goals.
“The magic was missing, that bit extra They defended well, fair play to them.
“We didn’t have the right ideas or the solutions. They weren’t there.
“Conceding the second goal was poor. So sloppy. We stopped getting out to the ball, and that’s completely out of character.
“No big inquest. We are disappointed. We have seen so many results this season out of character. Today, surprised, but with the world as it is we had been the most consistent side.
“We dust off the sad feeling and go again.”
Solskjaer said referee Peter Bankes made “two errors”. David De Gea was shoved by Billy Sharp as he tried to punch clear as Bryan scored.
And Anthony Martial had the ball in the net at the other end, but Maguire was ruled to have impeded Aaron Ramsdale who spilled the catch.
The United boss added: “First goal, it was a foul. The second (Martial’s), should be a goal. Inconsistencies. Two mistakes by the referee.”
Maguire said: “It wasn’t good enough, we didn’t play to the level we have in recent weeks.
“We gave them two goals, now it’s time to stand up and be counted because it’s easy when you are winning football matches – when you lose it is about how quickly you bounce back.”
Blades boss Chris Wilder said: “The players are jumping about in there and have every right to because it has been a tough season.
“Back to earth tomorrow and we go again playing the other side of town (Manchester City).”
Burke said: “Amazing result, amazing feeling and to get to goal. It will give us massive confidence. We showed great courage and determination.
“We fight for every ball and give 100 percent. We have been close this season but it has not gone our way.”
Sign up to the Mirror Football email here for the latest news and transfer gossip