Stuttering Marseille suffered their second defeat in four days on Friday, going down 1-0 at home to Nantes at the Stade Velodrome.
A solitary first-half strike from USA international Alejandro Bedoya gave Les Canaris their second consecutive win and lifted them above Marseille into fourth place in the table.
Marseille, who lost 1-0 at Lille on Tuesday, remain eight points adrift of the top three, with this latest setback further compromising their prospects of qualifying for next season's UEFA Champions League.
The gap from Elie Baup's side to Monaco in third could even increase with the principality side due to host struggling Ajaccio on Sunday.
A minute's applause was held before kick-off at the Velodrome in honour of former South African leader Nelson Mandela, who died on Thursday, while former Marseille striker Jean-Pierre Papin, one of the club's all-time great goalscorers who recently turned 50, was paraded to the crowd just prior to the start of the game.
How Marseille must wish they could call upon Papin at his peak now, as they toiled unsuccessfully to recover from the loss of Bedoya's early goal.
The former Rangers player converted a cutback from Filip Djordjevic in the 17th minute, with the ball dribbling into the net at Steve Mandanda's near post.
The hosts' best opening fell to substitute Saber Khalifa, who somehow blazed over the crossbar midway through the second half after excellent play from Andre-Pierre Gignac down the right wing.
Remy Riou in the Nantes goal also made two decisive interventions to deny Dimitri Payet in the second half, while Mandanda also saved well from Djordjevic at the other end.
But Les Canaris held on to inflict a damaging defeat on Marseille, whose under-pressure coach Baup oversaw Nantes's relegation from Ligue 1 during a spell in charge at the Stade de la Beaujoire in 2008/09.