All the key action took place in the space of two minutes around the interval as Lille's Florent Balmont saw red in first-half stoppage time before Jordan Ayew netted the only goal a minute after the restart.
OM move onto 26 points, level with PSG but second to the capital club on goal difference. Lille are ninth as their inconsistent campaign continues.
Marseille welcomed controversial midfielder Joey Barton into their line-up for the first time in Ligue 1 following the expiry of his 12-game domestic ban.
Bordeaux missed the chance to move top as Remy Cabella's goal midway through the second half gave struggling champions Montpellier a 1-0 victory.
The hosts started the game level with Sochaux, who occupied the third relegation spot, but Cabella's goal was just reward for their second-half display and gave them only a fourth win in 14 games, lifting them five places to 12th.
Lyon's annual capitulation at the Stadium Municipal saw Wissam Ben Yedder bag a brace as Toulouse climbed up to seventh in Ligue 1 with a 3-0 win.
Ben Yedder's double and Etienne Capoue's last-minute strike goal made it 11 goals conceded without reply from Lyon's last seven trips to the south west, as Remi Garde's men missed the opportunity to dislodge PSG from the top of the table.
Lyon, who remain in third place, had begun the game search of a first win on the road since the opening day of the season but they failed in that mission.