Manuel Pellegrini’s side were far from their clinical best at the King Power Stadium, but the winner from former Chelsea midfielder Lampard ensured the champions remain just three points behind his old club.
There was a significant blow for City however as captain Vincent Kompany, who had returned after a hamstring problem, was forced off with a recurrence of the same injury.
To make matters worse, City — who were already without Sergio Aguero due to a knee injury — lost another striker in the warm-up with Edin Dzeko pulling out to be replaced by youngster Jose Angel Pozo.
It was the bottom-of-the-table Leicester who had started the better with Esteban Cambiasso slicing off target after a driving run and Jamie Vardy having a shot deflected wide off Eliaquim Mangala.
An audacious 35-yard free kick from Cambiasso came close to catching out Joe Hart as Leicester dominated.
It took until the half-hour mark for City’s first chance when Pozo shot straight at Ben Hamer from the edge of the area after David Silva’s free-kick had only been half-cleared.
Moments later Hamer, in the side for the injured Kasper Schmeichel, made a decent stop to keep out a Yaya Toure drive from Silva’s pullback.
Pellegrini’s side were improving and went on to take the lead in the 40th minutes.
A patient build-up resulted in Samir Nasri crossing for Lampard to coolly flick home from six yards out.
It was the former England international’s sixth goal in 13 games since moving to Eastlands on loan from New York City.
- Flicked shot -
City nearly made it two early in the second half when Silva’s flicked shot just missed the target from Nasri’s cross.
Vardy then had a penalty appeal waved away as he went down under a challenge from Mangala.
Lampard was withdrawn on the hour to be replaced by James Milner, while Leicester manager Nigel Pearson took off Jeffrey Schlupp and sent on top scorer Leonardo Ulloa in a bid to spark his team into life.
Pearson was given a good reception by Leicester’s supporters in the club’s first home game since he had an angry confrontation with one of his own fans at the end of the 3-1 defeat by Liverpool earlier this month.
The Leicester boss faces a possible touchline ban after being charged by the Football Association over that incident, but the home fans were more concerned with trying to will their side to only their third league win of the season.
Kompany appeared to pull his hamstring again and was immediately replaced by Martin Demichelis late in the game.
Ulloa then saw a shot deflected wide as Leicester pushed for an equaliser before Mangala and Hart got in each other’s way to concede a corner.
City were left to hold on somewhat with Anthony Knockaert’s free-kick from 25 yards hitting the top of the wall.
For all their unstinting efforts, Leicester could not find the late equaliser with Ulloa blazing wide after Wes Morgan’s header down.