Marseille are fifth but are now eight points behind pacesetters Lille after 21 games.
At Monaco's Stade Louis II, Marseille dominated but failed to create clearcut chances against a Monaco side facing a battle to avoid relegation.
Earlier on Sunday, Girondins Bordeaux gave under-fire coach Jean Tigana a boost by securing their first league win since late November with a 2-0 victory over Nice.
Bordeaux moved up to eighth place, 11 points off the pace.
Defender Ludovic Sane scored the opener in the 38th minute, finding the back of the net from a corner at the near post, before Anthony Modeste put his team two-up just before the hour mark.
Tigana now has some breathing space after his future seemed to be in the balance following Bordeaux's embarrassing French Cup exit to second division Angers last weekend and a string of mediocre results since the beginning of the season.
"It was a very good match, Tigana told reporters. "It wasn't a reference but it was a good match. I simply hope we can do the same kind of performance against Lyon next week."
Montpellier beat Nancy 2-1 away to climb up to fifth place on 33 points.
Youssouf Hadji put Nancy ahead in the second minute but Souleymane Camara levelled six minutes later and defender Gary Bocaly put Montpellier ahead for good with a powerful shot from 30 metres.
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