Long-time leaders Lille drew 1-1 with Girondins Bordeaux on Saturday to drop points for the second straight game and Marseille's weekend was made even better by third-placed Olympique Lyon losing 1-0 at Paris Saint-Germain.
Hosts PSG had the better of the first half but Lyon were bossing the second until defender Zoumana Camara bundled the ball home on 77 minutes following a free-kick to send his side up to fourth, just a point behind their rivals.
Both sides, who also meet in next Saturday's League Cup final, were reduced to 10 men when Marseille's Loic Remy and Montpellier's Abdelhamid El Kaoutari were dismissed for a fracas after the award of the penalty.
"I'm especially happy because it was not an easy match," Marseilles coach Didier Deschamps told reporters.
"It was a victory where we showed heart, it wasn't easy because Montpellier defended very well."
They now face a fight to increase their meagre tally of 13 points and better Racing Lens' 1989 record of a lowest-ever French top-flight total of 17.
