Marseille climbed to fifth place in the Ligue 1, at the Stade Marcel Picot to extend its unbeaten streak in league play to five games.
With 31 points, Marseille slips one point in front of St Etienne and Toulouse, which are set to return to action in a full France schedule on Wednesday. St Etienne hosts PSG while Toulouse welcomes Brest.
Mathieu Valbuena and Stephane Mbia recorded goals in the first half for Marseille while Lucho Gonzalez tacked on a third in second-half stoppage time to put the result beyond any doubt.
Reynald Lemaitre provided the lone goal for Nancy, which remains just a point clear of the relegation zone with 18 points through 19 games.
Marseille has its work cut out for itself if it wishes to further extend its unbeaten run in league play, as it will host third-place Lille in its next league outing on Jan. 15, following a short winter break.
Nancy returns to action on Jan. 14 when it hosts Lorient.