Victory would have crowned City, who still hold a commanding 13-point lead over United, champions for a fifth time.
Paul Pogba sparked United’s recovery with two goals in three minutes early in the second half, with defender Chris Smalling grabbing the victor with a superb volley.
Kompany’s header and Guendogan’s clever turn and finish had City’s fans jumping as their team led 2-0 after half an hour. The Brazilian helped out his teammates with a number of timely interceptions but lost his head at times in the second half as United started mounting the pressure on the hosts.
The remarkable turnaround was complete when Smalling, badly at fault for Kompany’s goal, arrived unmarked to steer Alexis Sanchez’s free-kick past the exposed Ederson in the 69th minute.
Chris Smalling believes Manchester United laid down a marker for this season and beyond by preventing Manchester City sealing the Premier League with an astonishing comeback win.
Nev made the bold claim at half-time of the game at the Etihad. moments before Pogba’s brace to swing the game in United’s favour.
“If the accusation from his agent is that he wants to go to other clubs, his price has gone up”, said Mourinho wryly.
In a furious finale, players from both sides clashed and Ashley Young was fortunate that his wild lunge on City substitute Sergio Aguero in the area was ignored by referee Martin Atkinson.
Brilliant first half after that horror show during midweek against Liverpool and he proved his doubters wrong with a well-taken goal.
However, by fighting back United consolidated their place in second, four points clear of Liverpool, and sent a message that they can compete with City next season.
City could have clinched the Premier League title with six matches to spare, which would have set a record.
I have already told him that he can be the best in the world and [against City] can be the first step to achieve that because he is fantastic, and I think he needed a day like today.
Well, if the champagne was ready and the ice was frozen; then it was a sheer waste of money and excitement as Manchester City totally ruined the party mood that engulfed the stadium at halftime.
They face Liverpool on Tuesday in the second leg of their Champions League quarter-final tie at the Etihad.
His hair was dyed in City blue for the game but Pogba was very much a Red Devil.
The leggy midfielder did not look like a player who would cross Guardiola’s thoughts, either as a danger or potential acquisition, in a first 45 minutes in which United were dazzled and bewildered by City’s brilliance.
“In one month or one year we will see the game and think how did we lose it?”
Ilkay Gündogan then doubled City’s lead on 30 minutes when an absolutely lovely turn in the box.