The northerners, with a game in hand, have 32 points from 18 games and lead second-placed Paris Saint-Germain, who lost 2-0 at AS Nancy, by one point as the French top flight heads into a three-week winter break.
Third-placed Stade Rennes (31) slumped to a 1-0 defeat at lowly Caen while fourth-placed Olympique Lyon (31) were held 1-1 at home to Auxerre.
Champions Olympique Marseille failed to break the deadlock in a 0-0 stalemate at Brest and remained fifth, three points off the pace.
TITLE HOPES
Girondins Bordeaux's title hopes took a knock as the 2009 champions could only draw 2-2 with struggling RC Lens.
Captain Alou Diarra, who reduced the arrears after Eduardo and Razak Boukari had scored first-half goals for the visitors, was sent off with 19 minutes left, but Yoann Gouffran salvaged a point two minutes into stoppage-time.
Bordeaux are eighth on 27 points.
Lille thought they had the points in the bag in the 72nd minute when Moussa Sow netted his 14th goal from inside the box after being set up by Ivory Coast striker Gervinho but sixth-placed St Etienne responded swiftly.
France defender Adil Rami fouled Blaise Matuidi in the box and Bakary Sako converted the resulting penalty three minutes later.
Rudy Garcia's side piled the pressure on in the closing stages but Les Verts regrouped in their half and held on.
A point, however, was more than PSG and Rennes could manage on a night of below-par performances by the top sides.
PSG had defender Mamadou Sakho sent off in the first half for a minor foul after 14 minutes and Youssouf Hadji grabbed a second-half double to give Nancy all three points.
Rennes were caught snoozing after nine minutes at 18th-placed Caen, who prevailed thanks to Romain Hamouma's super curled shot from 20 yards out.
Marseille, who have picked only four points from their last five league games, collected a point at Brest - not enough for keeper Steve Mandanda.
"It is not what we were hoping for. This month of December is not catastrophic but almost...," the French international told French TV channel Foot Plus.
"We now must recuperate and come back stronger next year with more ambitions."
Lyon could have gone top of the standings had they beaten Auxerre, but Jean-Pascal Mignot's own goal on the stroke of half-time was cancelled out one minute into the second half by Julien Quercia.
Forward Quercia collected a fine defence-splitting pass from Dennis Oliech and dribbled past France keeper Hugo Lloris to score.
