Sochaux's Cedric Bakambu delivered another major blow to Lyon's title hopes as his 89th-minute winner left it eight points behind Ligue 1 leaders Paris Saint-Germain.
While Sochaux will celebrate Bakambu's strike for catapulting it out of the drop zone, the visitors' 2-1 win further derailed Lyon's hopes of reclaiming the league crown following a run that has now seen them without a win in four games and slip into third behind Marseille.
On a frustrating night for the hosts, that saw them hit the woodwork on three occasions, they looked like they might salvage at least a point when Bafetimbi Gomis' 69th-minute penalty cancelled out Giovanno Sio's opener.
But an unmarked Bakambu left them with no time for a second comeback after Sio's clever build-up play.
Sochaux's win, its first in six games since upsetting PSG, moves it two points clear of danger.
Marseille leapfrogged Lyon by beating Nice 1-0 for a first away win of the year in Nice.
A solitary first-half Andre-Pierre Gignac header was enough to claim all three points for the visitors and their first win in three saw them move seven points behind leaders Paris St Germain.
Lille maintained its push for a Champions League spot after beating struggling Brest 2-1 at the Stade Francis-Le Ble.
And with 11 minutes left Lille grabbed the winner through Nolan Roux to move them to within four points of third-placed Lyon.