The three points moved the big-spending capital club level on 63 points with Montpellier at the top of Ligue 1 - although the Parisians have played a game more.
PSG, who ended the game with ten men after a late red card for Mohamed Sissoko, made the ideal start as Jeremy Menez put them into the lead after just six minutes following good work by Brazilian Nene, who cut in from the left and set up a chance which Menez fired past Steve Mandanda.
Ghanian Andre Ayew got the equaliser after 59 minutes but PSG reacted straight away and two minutes later Alex Costa bagged his second goal for the Parisians.
The swift advantage was a boon for a PSG side on edge after last week's 2-1 loss at Nancy, which meant a first league defeat under coach Carlo Ancelotti.
"This match has given us confidence," said Ancelotti.
"After four games without a win it was very important to win again."
Sunday's win was only their third in their past nine outings.
Ancelotti sprang a surprise before kickoff in leaving strikers Guillaume Hoarau and Kevin Gameiro out of his starting line-up - though plenty of creative talent was there in the shape of Nene, Javier Pastore and Menez.
Ancelotti said: "We deserved this because we got off to a good start. We played our game and were solid for the 90 minutes even if Marseille put us under a lot of pressure."
"I'm disappointed though for Sissoko because he didn't deserve to be sent off."
A desperate run of form for 2010 champions Marseille means that they and coach Didier Deschamps - reportedly a summer contender for the Chelsea job - are set to miss out on a Champions League qualification, though they meet Lyon in next week's League Cup final.
France's only European champions stand just ninth - 16 points outside the top three.
Reigning champions Lille all but waved goodbye to their title after they conceded two goals in the opening ten minutes as they slumped to a 3-1 loss at a Brest side who moved three points clear of the relegation zone.
Lille's title push may have thereby suffered a fatal blow as they trail Montpellier by seven points having played a game more.
Ancelotti added: "Lille lost. For them it's going to be difficult to get back into the race. It will be a battle between Montpellier and PSG."
On Saturday, Montpellier, who have never won the title, saw off Sochaux 2-1 with Younes Belhanda and Souleymane Camara netting.
"We got the job done - we went out to grab a fine victory (but) we have to keep focused on the nine matches still to come," said Montpellier coach Rene Girard, a former France international who won three league crowns as a player with Bordeaux.
Fourth-placed Lyon trimmed back to three points their deficit on Lille after two goals from Lisandro Lopez saw off bottom side Auxerre 2-1.
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