Lille, who had picked up only two points in four games against Paris St Germain, Olympique Marseille and Olympique Lyon this season, snatched a 2-1 win at the Stade Velodrome last weekend to finally prove they were made of steel.
"Winning [against Marseille] at the Velodrome, against one of our rivals, is a huge morale-booster," Lille captain Rio Mavuba told the club's website.
Lille, who have 49 points from 26 games, should be too strong for 13th-placed Valenciennes who they host on Sunday, although the leaders have a doubt over Moussa Sow's fitness.
The Ligue 1 top scorer picked up a knee strain against Marseille last weekend but Pierre-Alain Frau, who netted the winner at the Velodrome, has already shown he can deputise.
Second-placed Stade Rennes, level on points with Lille, could lose ground in the title race as they face a test of their credentials at home to fourth-placed Marseille on Friday.
Once again, Rennes will rely on their sturdy defence, the best in the league with only 18 goals conceded.
"We are a solid team who try to get the ball high up the pitch although we are not Barca," coach Frederic Antonetti told France Football magazine.
"We try and get the ball 40 metres from our goal and we do it pretty well. Our attacks can be very swift."
Rennes could be without France holding midfielder Yann Mvila, who is doubtful with a knee injury, Antonetti told a news conference on Wednesday.
Marseille, who are four points off the pace, may have to make do without striker Brandao after the Brazilian was held by police for questioning over an alleged rape.
"Obviously, I could do without that kind of problem but the squad is going to focus on Friday's game. It's the most important thing," said coach Didier Deschamps.
Marseille will hope Argentine playmaker Lucho Gonzalez, who has been nursing a muscle injury, can play the 90 minutes.
Fifth-placed Paris Saint-Germain, whose title hopes took a knock last weekend when they slumped to a 1-0 defeat at lowly AJ Auxerre, host Montpellier on Sunday.
Coach Antoine Kombouare has therefore decided to rest midfielders Ludovic Giuly and Claude Makelele plus France striker Guillaume Hoarau for the first leg of their last 16 Europa League tie against Benfica on Thursday.
Third-placed Olympique Lyon visit Sochaux on Saturday.
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