Marseille were left counting the cost of Joey Barton's second-half dismissal as they slipped to a shock 1-0 defeat at home to lowly Nancy in Ligue 1 on Sunday evening.
The on-loan QPR midfielder was shown two yellow cards in the space of five minutes to leave OM facing an uphill struggle at the Stade Velodrome.
And an own goal from Andre Ayew capped off a miserable evening for the title hopefuls, who remain six points behind Ligue 1 leaders Paris Saint-Germain.
It marked only the third win of the season for Nancy, lifting them off the foot of the standings and within four points of safety.
Adrian Mutu scored twice as Ajaccio inflicted a blow to Lyon's title hopes with a shock 3-1 win.
Lyon's loss meant PSG retain their three-point lead at the head of the standings.
When Lyon edged ahead early in the second half through Alexandre Lacazette, it was all going to plan for Remi Garde's men.
But Ajaccio were soon level thanks to Chahir Belghazouani, before Mutu headed them ahead and added a late penalty, which also led to the dismissal of Lyon's Dejan Lovren.
Lyon earlier missed the chance to equalise from the spot when trailing 2-1, Bafetimbi Gomis seeing his effort saved by Guillermo Ochoa.
Reims remain in the relegation zone after squandering a first-half lead in a 3-1 defeat at Montpellier.
Gaetan Courtet put the visitors in front on 33 minutes, but Montpellier equalised just three minutes into the second half through Souleymane Camara and went on to claim all three points thanks to goals from Marco Estrada and Younes Belhanda.