Marseille made a horror start to 2013 as their Ligue 1 title bid suffered a shock blow with defeat at 10-man Sochaux.
OM returned from the winter break level at the top with Paris St Germain and Lyon but are adrift of both after a forgettable night in the snow in Montbeliard.
First-half goals from Sloan Privat and Cedric Bakambu stunned the visitors before a Jeremy Morel own goal shortly after half-time handed Sochaux full control.
Their grip loosened when Jordan Ayew quickly replied and then Joseph Lopy saw red on the hour.
But Marseille failed to make any further inroads with Lucas Mendes' header against the post with the final touch the closest they came.
Victory catapulted Sochaux, who were winless in six, out of the drop zone.
Marseille were without striker Loic Remy after it was confirmed before kick-off that the club had accepted an offer from Newcastle for the France international.
In his absence the OM strikers saw precious little of the ball as Sochaux deservedly took a 2-0 lead in thick snow.
Steve Mandanda had already been forced to punch away a Privat shot before the striker headed in Sebastien Roudet's cross after 17 minutes.
Souleymane Diawara's diving header hit the post at the other end but Sochaux went 2-0 ahead on 40 minutes.
Mandanda initially did well to clear Privat's ball into the area but Bakambu thumped the rebound past the stunned goalkeeper.
It got worse for OM just a minute after the break when Roudet's cross across the six-yard box was awkwardly kneed into the net by a back-tracking Morel.
Jordan Ayew pulled a goal back, when he smashed into the top corner on 55 minutes and Sochaux began to wobble soon after when Lopy was handed a second caution.
Lopy recklessly dived in on Mathieu Valbuena and deservedly saw red.
Marseille failed to make enough of an impression with an extra man, however, with Morel seeing a low drive saved before Mendes headed against the post in injury-time.