PSG claims derby spoils over Marseille
PSG, which hadn't won in three league games, took an early lead when winger Jeremy Menez curled the ball into the bottom corner after some poor defending from Marseille in its penalty area.
Ghana forward Andre Ayew headed in Marseille's equalizer in the 59th minute, but Brazilian defender Alex rose to nod in a corner two minutes later to give PSG a vital win.
Montpellier can move three points clear of PSG if it wins its game in hand away to Marseille on Wednesday.
Marseille's miserable slump continues, and coach Didier Deschamps' team has now lost 10 and drawn one of its past 11 matches.
Earlier, winger Anthony Mounier scored his eighth goal of the season as Nice beat visiting Lorient 2-0 to ease its relegation worries.
Mounier scored just after halftime and central defender Renato Civelli grabbed the second in the 57th minute as Nice moved up to 13th place.
Lorient's chances of making a comeback were all but over after midfielder Alaixys Romoa was sent off in the 78th.
Caen also secured an important win, beating Bordeaux 1-0 at home thanks to veteran midfielder Nicolas Seube's early goal to move out of the relegation zone. Lorient slipped below Nice and Caen and into the bottom three.