Top scorer Erling Haaland was absent through injury, missing his first game of the season, which saw City lack their usual cutting edge.
It was clear it would take something special to unlock the determined hosts, with Belgian midfielder De Bruyne stepping up, firing an unstoppable free kick into the net four minutes after the break to put City in front.
Leicester responded well and has a chance to level through a stunning volley from Youri Tielemans, but City goalkeeper Ederson brilliantly tipped the thunderbolt of a strike onto the crossbar.
The hosts kept coming, putting City under plenty of late pressure, but the champions held on to climb back to the top of the standings on 29 points, one clear of Arsenal who play Nottingham Forest on Sunday. Leicester stay 17th.
Additional reporting by Reuters.