Lyon suffered their first defeat of the season after going down 1-0 at Rennes.
Stephane M'bia Etoundi scored the only goal of the game on 13 minutes at La Route- de-Lorient.
Any hope Lyon had of getting back into the game went up in smoke when playmaker Juninho Pernambucano was sent off 12 minutes from time.
The defeat for Gerard Houllier's side will give hope to the chasing pack in Ligue 1.
Second-place Lille took advantage of Lyon's slip-up with a 3-0 win at promoted Valenciennes.
Goals from Nicolas Fauvergue (24), Peter Odemwingie (61) and Yohan Cabaye (90) saw Claude Puel's side recover from their UEFA Champions League defeat at AEK Athens in midweek.
Sochaux moved level on points with Lille with a 1-0 home win over ten-man Troyes.
Guiranne Ndaw (68) scored the only goal of the game at Stade Bonal, as struggling Troyes had Gregory Paisley sent off for two bookable offences.
Marseille missed the chance to close the gap on Lyon after going down to a 1-0 home defeat to promoted Lorient.
The impressive Pierre-Andre Gignac (48) silenced the Stade Velodrome crowd with his winner for the visitors.
A brace from Vincent Hognon (10, 85) and single strike from Bafetimbi Gomis (22) gave St Etienne a 3-0 home win over former manager Elie Baup and his current club Toulouse.
Ismael Bangoura was the hero for Le Mans, as his hat-trick claimed a dramatic 3-2 win at Auxerre.
He opened the scoring on 14 minutes before Auxerre struck with goals from Kanga Akale (56) and a Luigi Pieroni penalty (79).
Bangoura equalised a minute later before Auxerre had Younes Kaboul sent off for two bookable offences.
A minute into injury time, Bangoura was on hand to claim his third goal and the three points for Le Mans at Stade Abbe-Deschamps.
South of France rivals Monaco and Nice had to settle for a goalless draw at Stade Louis II, while Sedan held Nantes to a 1-1 home draw.
Dimitrie Payet (43) gave Les Canaris the lead before Gregory Pujol (62) earned a share of the spoils for Sedan.
Click below for match summeries:
Auxerre 2-3 Le Mans
Marseille 0-1 Lorient
Monaco 0-0 Nice
Rennes 1-0 Lyon
Sedan 1-1 Nantes
Sochaux 1-0 Troyes
St Etienne 3-0 Toulouse
Valenciennes 0-3 Lille