Manchester City boss Mark Hughes is demanding an explanation from the referee after United striker Michael Owen settled the Manchester football derby in the 96th minute.
Owen sealed a thrilling 4-3 win for United, despite the fourth official having indicated just four extra minutes would be played.
Hughes feels the pressure of the home Old Trafford crowd may have got to the referee.
Meanwhile Chelsea have beaten Tottenham Hotspur 3-nil to remain three points clear of Manchester United in the English premiership.
While Wolverhampton climbed away from the relegation zone with a 2-1 win over Fulham, and Everton beat Blackburn 3-nil.