Paul Pogba sparked United’s recovery with two goals in three minutes early in the second half, with defender Chris Smalling grabbing the winner with a superb volley.
“At halftime we were feeling sorry for ourselves, we wanted to go out there and play with prided and thought we full deserved it in the end,” Smalling told Sky Sports.
“The first half was terrible, we dropped off didn’t play our game, and could have been out of sight.”
In those opening 45 minutes City looked to be effortlessly on course to clinch a new English Premier League record by becoming the quickest team to win the title.
Pep Guardiola’s team were dominating proceedings against the league’s second-place team and took control of the game with two goals in the space of five minutes.
Captain Vincent Kompany shook off his marker Smalling to power a header past United goalkeeper David de Gea and then Ilkay Gundogan displayed neat footwork before slotting home the second.
United were being outclassed and if Raheem Sterling had been more assured City might have gone in at the break perhaps four goals ahead.
Just before United’s remarkable revival Gundogan also hit the woodwork.
Blow for City
Pogba’s season has been interrupted by injury and the French international hasn’t scored a league goal for United since November, but he made amends in some style with those goals early in the second half to wrestle control of the game away from City.
“You never see Paul hide, 11 players stood up today when it would have been easy to hide,” added Smalling.
Six years ago, City were crowned Premier League champions on the last day of the season after beating QPR 3-2 with Sergio Aguero scoring a stoppage-time winner.
Guardiola brought on the Argentine after Smalling’s goal, but there was to be no repeat heroics from Aguero, though he did force a wonderful one-handed save from De Gea with a header.
This was the only the second time City has lost in the league this season.
“Our challenge is to finish second but I want to congratulate City for the title because they are going to win and deservedly,” Mourinho told Sky Sports. “They gave no chance to the others because they had this season of don’t stop winning.
“My objective here was to get points and not spoil any celebrations. The point is can we improve enough to catch them next season?”
City must now wait until the weekend of April 13/14 to see if they can claim their third league title in six years.
Guardiola’s team need to win at Spurs next Saturday at Wembley Stadium and hope United drop points against West Brom the following day.
The manner of Saturday’s defeat was also a blow for City, who in midweek were thumped 3-0 by Liverpool in the first leg of their Champions League quarterfinal.
The second leg is at the Eithad on Tuesday.
Guardiola told Sky Sports he was “a little sad for fans and players,” adding “we will try to be in a good mood next Tuesday.”