Bordeaux slipped out of the top four after slumping to defeat at improving Ajaccio, who followed up their surprise win over Lyon last weekend with another impressive scalp.
A first-half strike from Ricardo Faty was enough to earn Ajaccio the spoils as Bordeaux suffered only their second defeat in 13 matches in all competitions.
The loss sees Bordeaux drop to sixth in the standings, with St Etienne taking their spot among the European places.
Ajaccio, meanwhile, are up to 14th after extending their unbeaten run to five matches in Ligue 1, which has also included holding title favourites Paris St Germain to a draw.
Les Girondins, who face Dynamo Kiev in the first leg of their Europa League last-32 tie on Thursday, came into today's match having won five of their last six in league and cup and they enjoyed the better of the early exchanges at the Stade Francois Coty.
David Bellion saw his goal-bound volley deflected away by home defender Ronald Zubar before Fahid Ben Khalfallah's effort from a Ludovic Obraniak cross flew just wide.
Ajaccio had produced little to worry Cedric Carrasso in the visiting goal in the opening half-hour, but when they finally created a decent chance they made the most of it as Faty opened the scoring in the 32nd minute.
Bordeaux struggled to properly clear a Johan Cavalli free-kick, allowing Faty the chance to head the loose ball past Carrasso.
That proved to be the match-wining effort, although Bordeaux came close to an equaliser on more than one occasion.
Guillermo Ochoa denied Julien Faubert before the break at the expensive of a corner while the home goalkeeper did superbly to keep out Bellion's deflected shot at the start of the second half.
Ochoa also performed heroics in the 72nd minute to save Nicolas Maurice-Belay's close-range shot.
Ajaccio were again causing little danger at the other end but they came within inches of doubling their lead in the 78th minute when Adrian Mutu's volley smashed against the post.
Bordeaux had one late chance to snatch a point but again Ochoa stood in their way, the Mexico international deflecting Maurice-Belay's well-struck effort away with his thigh.