Marseille's stunning start to the Ligue 1 season, which saw them win six from six games, came to a spectacular end as mid-table Valenciennes whipped them 4-1.
A double by Anthony Le Tallec and one apiece from Foued Kadir, gifted to him by Marseille goalkeeper Steve Mandanda, and a brilliant opener by Gael Danic gave Valenciennes the points, with Jordan Ayew scoring a consolation.
Marseille, who were going down to their first defeat in all competitions this season as they had drawn three and won two of their UEFA Europa League games, still top the table, leading Paris Saint-Germain by three points, although Lyon can pull to within one if they beat Bordeaux at home later on Sunday.
Marseille had only conceded one goal in all Ligue 1 games this season prior to the game but went behind in the 16th minute with a superb free-kick by Danic, although Mandanda let rip at his wall, which he felt should have jumped higher.
Le Tallec, who numbers unsuccessful spells at both Liverpool and Sunderland among his many clubs, doubled the lead in the 35th minute by putting away a superb cross by Danic.
Any hope Marseille had of regrouping at the break disappeared when Mandanda completely fluffed a throw out from inside his area which landed at Kadir's feet just outside the box and he put it away with the Marseille goalkeeper vainly trying to regain his position.
Le Tallec added his second in the 65th minute with a header from another Danic cross to send the record attendance of just over 22,000 wild and give Marseille plenty to think about ahead of their home game with bitter rivals PSG next Sunday.
For Valenciennes, it maintained their hold over Marseille, who have beaten them just once since the former were promoted in 2006.
Marseille coach Elie Baup said: "Nothing worked for us or went right for us. To go in 3-0 down at half-time gave us no way back. The verdict this evening is a heavy one, brutal, and will have ramifications.
"We will talk about it among ourselves and work on things during the week. However, we should not dwell on such a heavy defeat forever. We should look ahead and think about our next challenge and how to put things right."