City couldn't afford to drop points with Liverpool breathing down the necks of the defending champions.
Plus United's recent run of wins at the Etihad added another factor to this meeting of the Manchester tribes.
But it was City who struck early through Kevin De Bruyne before Jadon Sancho levelled for the Reds.
De Bruyne restored City's lead shortly after, but the game was still on a knife-edge.
The second period, however, belonged to City.
United were swept aside as Riyad Mahrez added two more to complete a stunning 4-1 win.
Enjoy the extended highlights of the game on the video above...