Saint-Germain lost only for the second time this season, when it fell against Nantes, on Saturday, to give Marseille the opportunity to reduce the 13-point difference with the summit.
But Clement, promoted to the top flight, spoiled this scheme, and advanced with an early goal from Mohamed Bayo, then added a goal near the end by heading substitute Jim Alvina after a corner kick.
Marseille’s tally stood at 46 points, just one point behind third-placed Nice, who beat Angers 1-0 earlier on Sunday, thanks to a goal from Justin Kluivert.
Nice could have won more goals, but he missed a lot of chances.
Fourth-placed Strasbourg scored one point away from home in a 2-2 draw with struggling Saint-Etienne, who scored a goal from Tunisia international Wahbi Khazri.
Saint-Etienne spent most of the season in the relegation zone, but this draw raised his score to 22 points, and advanced to the safety zone.
Saint-Etienne is 16th, one point ahead of the bottom four of Troyes, Lorient, Metz and Bordeaux.
