Marseille remain unbeaten in five domestic games under Jose Anigo after coming from behind to beat Evian 2-1 while Lille blew a chance to go second as they lost 2-1 to Reims.
On-loan winger Pape Amodou Sougou put Marseille in front against his parent club, but Benoit Cheyrou equalised for OM and Andre-Pierre Gignac netted what turned out to be the winner before the interval.
It was Marseille's first-ever win away to Evian and the three points lifted them back up to fifth place in the Ligue 1 table.
Lille meanwhile suffered only their second home defeat of the season as they slumped to a 2-1 loss against Reims, where Odair Fortes and Grzegorz Krychowiak hit second half goals.
Anthony Weber put the ball through his own goal to give Lille hope with two minutes left but it was too little, too late as the Champagne-region outfit held on for their eighth victory of the season.
The defeat, only Lille's fourth in 20 outings, keeps them third and seven points back of leaders Paris Saint-Germain while Reims climb above Bordeaux and Nantes into a tie with Marseille for fifth place.
Marseille remain eight points adrift of the Champions League qualification places despite their key win at Evian.
Last summer, OM raided Evian to sign their Tunisian international forward Saber Khalifa, with Senegalese winger Sougou moving in the opposite direction on a season-long loan deal.
Both players featured prominently at the Parc des Sports, with Sougou meeting a left-wing corner to send a looping header over goalkeeper Steve Mandanda and into the net at the far post on 15 minutes.
It was his fourth league goal of the season, although he refused to celebrate against the club to whom he still belongs.
The visitors were level within seven minutes, though, as Cheyrou collected a loose ball in a central position 25 yards from goal and curled a beautiful shot over 'keeper Bertrand Laquait and into the net.
Gignac then made it 2-1 in the 38th minute, heading in his sixth goal in five games in all competitions from a clipped Florian Thauvin cross.
OM had chances to increase their lead in the second half, notably when Khalifa hit the bar as he attempted to lob Laquait from 30 yards.
However, they held on to claim what was their first win in the league since late November, while the defeat leaves Evian just three points above the drop zone.
Earlier, Nantes beat local rivals Lorient 1-0 at the Stade de la Beaujoire, Ismael Bangoura firing home his first goal for the club since May 2012 to seal the points with just a minute remaining.
Yann Jouffre hit the bar from a free-kick in stoppage time for Lorient, who suffered a first defeat in eight Ligue 1 games.
Nantes are sixth after the win, and the impact of the Guinean Bangoura was particularly welcome.
The southern Brittany side face the prospect of a FIFA-imposed transfer ban, of at least a year, for allegedly going against the rules with their signing of Bangoura from Emirati club Al Nasr in 2012.
That could prove particularly damaging if this season's eight-goal top scorer Filip Djordjevic, who set up Bangoura's goal against Lorient, leaves as expected when his contract expires in the summer.
PSG were not at their best away to Ajaccio on Saturday, but still came from behind to win 2-1 against the division's bottom club thanks to goals by Ezequiel Lavezzi and Blaise Matuidi.
Monaco were held to a 1-1 draw at Montpellier on Friday.