Nancy kept up the pressure on league leaders Lyon with a 2-1 win at home to Bordeaux, while Lens are fourth following a 3-1 victory at Paris Saint Germain.
Sebastien Puygrenier (15) put Nancy ahead in a pulsating first half at the Marcel Picot.
Jean-Claude Darcheville (31) then equalised for the visitors, before referee Herve Piccirillo decided to award ASNL a decisive penalty after the restart.
To the delight of the home crowd Moncef Zerka (54) stepped up to slot the ball home and earn his side a valuable three points.
Lens meanwhile had Daniel Cousin to thank for their second half comeback at the Parc des Princes.
Sylvain Armand had put the home side ahead on 27 minutes before Cousin (50, 68) struck twice after the break and Olivier Thomert sealed the result with his strike 10 minutes from time.