The Bulgarian striker headed home shortly before the hour as Monaco remained fifth with 39 points from 22 games, six behind leaders Olympique Lyonnais, who host lowly Metz on Sunday (1300 GMT) and two points off the Champions League spots.
Monaco went into the game having conceded one goal in their last 11 matches in all competitions and with mid-table Lille taking no chances they were barely threatened throughout.
The visitors dominated possession but could not manage a single shot on target in a poor first half.
Lille suffered a setback in the 40th minute when defender Franck Beria came off with what looked like a knee injury and was replaced by Sebastien Corchia.
Monaco were more dangerous after the break with Joao Moutinho's low shot going just wide two minutes into the second half.
Berbatov was more accurate when he beat Vincent Enyeama with a fine header from Yannick Ferreira Carrasco's free kick with Monaco's first attempt on target.
On Friday, second-placed Olympique de Marseille lost 2-1 at Nice to remain a point behind Lyon. Champions Paris St Germain, four points off the pace in third, travel to fourth-placed St Etienne.
(Reporting by Julien Pretot; Editing by Ken Ferris)
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