Marseille leapfrogged Lyon into second place in Ligue 1 following an impressive first away win of the year in Nice.
A solitary first-half Andre-Pierre Gignac header was enough to claim all three points for the visitors and their first win in three saw them move seven points behind leaders Paris St Germain.
A third defeat in four meant Nice missed a great opportunity to move up to fourth and with it put a large dent in their Champions League aspirations.
Nice were first to go close inside 10 minutes when Eric Bautheac's superb volley from the edge of the area brought a solid save out of Steve Mandanda.
But Marseille's early dominance paid off on the quarter-hour. Mathieu Valbuena's run and shot was deflected away but the diminutive Frenchman picked out Gignac at the near post from the resulting corner and he headed beyond David Ospina to open the scoring.
Nice nearly hauled themselves back into the game when Rod Fanni headed Jeremy Pied's free-kick towards his own goal but the defender was lucky to see the ball come back off Mandanda's left post.
Ospina was called into action with 30 minutes played when Gignac found himself one-on-one but his left-footed effort was turned away by the Mexican.
Nice did have the ball in the back of the net before the break but Dario Cvitanich was rightly ruled offside.
The hosts came out with intent following the interval and went close twice in the space of a minute.
First Bautheac met the impressive Pied's cross with his head but failed to find the target before Camel Meriem brought a save out of Mandanda with a rasping 30-yard drive.
The intensity shown in the early part of the match began to die off but Timothee Kolodziejczak managed to get a decent 25-yard volley on target without really testing Mandanda.
With 15 minutes left, Nice were given an opportunity to draw level. Bautheac was brought down on the edge of the area and Didier Digard powered the resulting free-kick direct at goal but the wall did its job and deflected the ball out for a corner.
Shortly after Benoit Cheyrou appeared to handle the ball under pressure from Pied in the area but Nice's penalty claims were waved away.
Marseille wasted a late opportunity to double their lead when Andre Ayew miscued following a counter attack but the visitors had already done enough to claim the three points.