Olympique de Marseille's second place in Ligue 1 came under threat on Saturday when they slumped to a 2-1 home defeat against in-form Stade Brestois.
Marseille wasted their first-half advantage earned through Gerson's goal as Romain Faivre and Franck Honorat inspired the visitors to a remarkable comeback win, their team's sixth in succession.
After failing to win any of their first 11 games, Brest have now picked up a maximum 18 points in six outings and jumped up to sixth on 24 points from 17 games.
OM have 29 points and trail leaders Paris St Germain by 12 points before the capital side's game at RC Lens later on Saturday.
Third-placed Stade Rennais are a point behind and fourth-placed Nice are two points adrift before playing on Sunday.
At the Stade Velodrome, the hosts got off to a solid start and Gerson put them ahead with a fierce strike into the top of the net after a one-two with Dimitri Payet on 29 minutes.
Brest, despite enjoying very limited possession, made the most of their chances after the break.
Boubacar Kamara handled the ball in the area and, after a VAR review, the visitors were awarded a penalty that Faivre coolly converted to equalise in the 53rd minute.
In the 70th, Honorat was played through by Jeremy Le Douaron before beating Pau Lopez with a brutal shot that went in under the bar.
