Marseille's early-season troubles resurfaced on Friday as Sloan Privat and Nicolas Benezet fired Guingamp to a 2-0 victory over Michel's side in Ligue 1.
Privat made up for a missed penalty when he fired home the opening goal with 18 minutes to play at Stade du Roudourou, following superb work from Jimmy Briand.
And after Marseille had seen a Mario Lemina strike disallowed, Benezet wrapped up Guingamp's first win of the season with a fine finish from distance.
The hosts were handed a glorious opportunity to opening the scoring inside three minutes when Lassana Diarra felled Briand inside the penalty area, but Steve Mandanda was on hand to save Privat's weak spot-kick.
Guingamp continued to look threatening prior to the interval and went close as Mustapha Diallo placed a free header wide of goal.
Marseille - who beat Troyes 6-0 last weekend but have now lost three of their opening four league matches - also threatened but lacked quality in their finishing, Michy Batshuayi and Remy Cabella both guilty of wasting good chances.
Eventually Guingamp found a way through as Briand jinked past two defenders and - with the goalkeeper drawn - squared to Privat, who calmly slotted home.
Batshuayi's strength and persistence created another Marseille opening almost immediately, but the next goal came Guingamp's way as Benezet curled a 20-yard strike past Mandanda to leave Michel to ponder his first defeat since succeeding Marcelo Bielsa.
