Marseille went five points clear at the top of Ligue 1 on Wednesday, while Le Mans kept their survival hopes alive by upsetting Bordeaux.
Marseille travelled to lowly Sochaux with a two-point advantage at the top of the table and a game in hand over second-placed Auxerre.
It looked as though the Mediterranean giants, chasing their first league title since 1992, would squander the opportunity to pile the pressure on their rivals.
But Stephane Mbia struck just two minutes from time to give Marseille a 1-0 victory.
The defender secured the club's fifth straight win by following up after Sochaux goalkeeper Matthieu Dreyer had failed to gather his close-range effort.
Le Mans condemned defending champions Bordeaux to a third straight league defeat by claiming a much-needed 2-1 home win.
The hosts came into the game 13 points adrift of fourth-bottom St Etienne and defender Carlos Henrique headed Bordeaux into an eighth-minute lead.
But Anthony Le Tallec drew Le Mans level in the 16th minute before midfielder Mathieu Dossevi netted the winner a minute before the break.
The Ligue 1 strugglers had Fousseyni Cisse sent off eight minutes from time for a second booking but hung on for their first win in seven.
That puts Le Mans 10 points from safety with six games left while Bordeaux's hopes of defending their title look over.
Laurent Blanc's men remain fifth, two points behind fourth-placed Montpellier and although they have a game in hand on table-topping Marseille, they are now nine points off the pace.