Lyon ended Marseille's eight-match winning run in Ligue 1 with a 1-0 triumph at the Stade de Gerland on Sunday night.
Yoann Gourcuff's 64th-minute strike against the run of play was enough to steer Les Gones to victory over the league leaders.
l'OM, who have won eight of their first 11 matches, are four points clear of second-placed Paris St Germain at the top but Lyon are now up to third and five points off first place themselves.
Lyon made a positive start and Gourcuff looked to test the Marseille defence early on with a couple of dangerous deliveries from free-kicks, but Marcelo Bielsa's team stood firm before Christophe Jallet found himself in a shooting position only to fire over.
However, it was Marseille who went closest to scoring early on with their first real chance but Andre Ayew's curling effort from the edge of the area was matched by Anthony Lopes' diving save.
Then, Benjamin Mendy found himself free on the right but Florian Thauvin was unable to capitalise on his delivery to the back post, volleying wide of Lopes' goal.
Despite dominating possession, Lyon were struggling to create chances and it was l'OM who went close again after the restart but Andre-Pierre Gignac saw his stinging effort turned away once again by Lopes.
The visitors continued to knock on the door and next up Mendy went even closer to beating Lopes but his side-footed effort from 16 yards came back off the post before Gignac fired wide of the target on the follow up.
Lopes was called upon again, this time pulling off his best save of the evening to deny Ayew after Thauvin had superbly picked out the Ghanaian before Lyon took the lead against the run of play.
Alexandre Lacazette was the provider and his pass found Gourcuff who burst into the box before coming back on to his left foot and powering an emphatic shot beyond a sea of bodies to give the host an undeserved advantage on 64 minutes.
Bielsa's men tried to offer an instant response but, when Thauvin picked out Ayew from a corner the latter could only fire wide with a first-time header.
As the clock ticked away it was Lyon who looked the more likely to get a second, with Lacazette going close after a powerful run but his shot was gathered low down by Steve Mandanda at the second attempt.
Substitute Clinton N'Jie was the next to test Mandanda, this time in stoppage time, but in the end it was the hosts who secured all three points.
