Valere Germain and Emmanuel Riviere scored either side of the interval to put the team from the principality on 48 points from 22 games.
Paris St Germain, who will travel to the Louis II in two weeks time, have 51 after conceding a 1-1 draw at En Avant Guingamp on Saturday.
Falcao's season could well be over as the Colombia striker underwent surgery on Saturday on a damaged left knee ligament.
His team mates, however, did the job with a solid performance against OM, who slipped down to ninth on 32 points.
Germain put the hosts ahead four minutes before the break, outspeeding Souleymane Diawara before beating Steve Mandanda with a low, diagonal shot.
In the 57th minute, Riviere found the back of the net after collecting Geoffrey Kondogbia's defence-splitting pass to double the tally.
St Etienne stayed fourth on 37 points despite losing 2-0 at Girondins Bordeaux, who moved up to sixth on 34 after Abdou Traore and Henrique gave them a straightforward win.
Olympique Lyon, now fifth also on 34 points, snatched their third consecutive league victory by beating Evian Thonon Gaillard 3-0.
(Reporting by Julien Pretot; Editing by Rex Gowar)
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