Marseille was left counting the cost of Joey Barton's second-half dismissal as it slipped to a shock 1-0 defeat at home to lowly Nancy in Ligue 1 on Sunday night.
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 St. Germain.
It marked only the third win of the season for Nancy, lifting it 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 retains its 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.
Reims remains 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 equalized 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.