Montpellier once again benefited from a sterling performance by Younes Belhanda, who struck a double, including a superb volley into the top corner as the visitors claimed their first win at Marseille from 21 attempts with Olivier Giroud also on the scoreboard.
After handing Marseille their 11th defeat in 12 outings in all competitions, Montpellier moved up to 66 points with seven games left. Second-placed Paris Saint-Germain's are on 63.
Olympique Marseille's largest fans group, the South Winners, had asked their team to lose against Montpellier in order to prevent arch rivals PSG from clinching the title.
"Stay true to yourselves... lose", claimed a banner in the Stade Velodrome.
Marseille levelled on 33 minutes through Stephane Mbia's downward header from a Benoit Cheyrou free-kick.
