Lyon lead second-placed Paris St Germain, who were held to a goalless draw at Grenoble, with Toulouse third seven points off the pace following a 0-0 draw at home to Valenciennes.
PSG dominated throughout at the Stade des Alpes but Stephane Sessegnon, Ludovic Giuly and Guillaume Hoarau proved too clumsy in the area, just like Toulouse striker Andre-Pierre Gignac, the top scorer in Ligue 1.
Three days before hosting Barcelona in the Champions League, Lyon showed composure, although not great football.
They were barely troubled and went ahead after 19 minutes when Cris headed home from a Cesar Delgado corner.
Lyon sat on the advantage and survived a penalty scare six minutes into the second half. Keeper Hugo Lloris parried Youssouf Hadji's kick from the spot after Lamine Gassama had fouled Jonathan Brison.
In the last minute, Cameroon midfielder Jean Makoun set Benzema up with a perfect cross and the France striker coolly slotted the ball past Nancy keeper Gennaro Bracigliano.
Stade Rennes stayed in the race for a Champions League berth with a 1-0 win at Nice. Midfielder Olivier Thomert met a Jimmy Briand cross in the box to score in the 67th minute.
Rennes are sixth, three points behind Toulouse, who occupy the last Champions League qualifying spot.
Relegation is looming for bottom club Le Havre, who lost 2-1 at home to AJ Auxerre and, with 15 points, they are now 10 from safety with 13 matches remaining.
Olympique Marseille will have the opportunity to reduce Lyon's lead to five points when they host Le Mans on Sunday.
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