Marseille failed in its bid to join Lyon at the Ligue 1 summit on Sunday as the club sustained a 3-1 defeat at relegation-battling Sochaux.
A run of three successive wins placed Marseille among the joint leaders heading into the weekend, but after a draw for PSG and a Lyon victory, Marseille now finds itself in third place.
Sochaux came into the game at the opposite end of the table, having lost its last three.
However, the home side took control from the start and went in front after 18 minutes when Sloan Privat headed home a cross from Rafael Dias just a few yards from the net.
The lead became two goals five minutes before halftime when Cedric Bakambu found himself on the other end of a flicked header from Mathieu Peybernes, allowing the midfielder to score from close range.
Things got worse in the opening minute of the second half for Marseille after an own goal from Jeremy Morel, while Jordan Ayew provided the lone positive moment for the visitors with his fifth goal of the season in the 55th.
Sochaux had to play the final 29 minutes with 10 men after Joseph Lopy was sent off, but the hosts had little trouble and were able to move out of the bottom three on goal difference.
Nice rolled over Valenciennes, 5-0, with two goals from Dario Cvitanich, while Bastia secured a 2-1 win at Reims to climb six points above the relegation places.