United ground out a hard-earned derby victory at neighbours City to put the pressure on second-placed Chelsea who need to win at Arsenal on Sunday to keep their Premiership hopes alive.
The 136th meeting of these two teams proved to be one of the less memorable Manchester derbies and was settled by a first-half penalty from Cristiano Ronaldo as City's miserable home campaign finished on a losing note.
Indeed, City have not won or scored a league goal at Eastlands since New Year's Day, an incredible time span of 738 minutes.
They even missed a penalty for the second successive home game as they again lost their bearings in front of goal.
And their record of ten League goals is the lowest ever home total in the history of English top-flight football. To make matters even worse, only 26 League goals have been scored in total at Eastlands this season.
City were also fortunate not to have Michael Ball sent off after only two minutes. The left-back stamped on the chest of Ronaldo when he lay on the ground after a challenge.
The incident was caught on TV but missed by the referee, Rob Styles, and the other match officials.
United were unfortunate not to take the lead midway through the opening period when central defender Rio Ferdinand stole in unmarked at the far post to head against the crossbar.
They finally made the breakthrough in the 34th minute when Ronaldo exacted revenge on Ball by drawing a foul from the former Everton and Rangers defender inside the penalty area.
Ronaldo confidently stepped forward to score from the spot, his 23rd goal of the season.
City rarely troubled United in the second half with Edwin Van der Sar's only save of note, a diving stop to deny Emile Mpenza.
The second half petered out as United were happy to sit on their one-goal lead while City didn't have the know-how to break through their opponents defence.
There was a dramatic final twist though when City were awarded an 80th-minute penalty when Ball was adjudged to have been fouled by Wes Brown, although TV replays suggested there was no contact.
Darius Vassell stepped up to take the penalty but Van der Sar saved his spot-kick with his legs as City's goal drought at home continued.
The final whistle was greeted by wild celebrations from the United players and staff as they knew the Premiership title was all but won.