Cheick Diabate struck a late winner as Bordeaux increased Nancy's relegation fears at the Stade Jacques Chaban-Delmas.
Nancy had looked on course for a miraculous escape from the drop after picking up 17 points from a possible 24 recently, having previously won just twice in 25 league matches, but they lost 3-0 at home to Lyon last week and suffered more disappointment tonight.
Nancy appeared to have snatched a point when second-half goals from Loosemy Karaboue and Salif Sane cancelled out two Bordeaux goals in the final five minutes of the first half from Andre Biyogo Poko and Henri Saivet.
But there was a late twist in the tale as Diabate popped up four minutes from time to earn Bordeaux the victory.
The hosts, who cannot finish any higher than the seventh place they currently occupy, went close early on when Sane squandered possession in midfield but, after combining with Diego Rolan, Poko's powerful strike was well saved by Damien Gregorini.
Bordeaux went close again on the half-hour mark, but Rolan's effort went just wide after Benoit Tremolinas showed great skill to create the opening.
With an apparently goalless first half drawing to a close, Bordeaux's dominance finally paid off with a quickfire double.
Firstly, Julien Faubert's volley following a corner was kept out by Gregorini, but Poko was on hand to pounce on the rebound to make it 1-0
Then, on the counter, Bordeaux doubled their lead when Ludovic Obraniak rolled the ball into the path of Saivet to fire past Gregorini.
Bordeaux almost made it three on the hour mark when Rolan saw his effort from inside the area kept out by the busy Gregorini and that miss proved telling when Nancy pulled a goal back just a minute later.
Yacine Jebbour found Karaboue on the edge of the area and his seemingly tame shot crept through the legs of Cedric Carrasso and into the net.
Gregorini made yet another great save from a long-distance Poko effort and his performance paid off when Nancy equalised with 10 minutes left to play.
Thomas Mangani took charge of a free-kick on the right and picked out an unmarked Sane at the back post to head beyond Carrasso.
However, heartbreak struck for the visitors when Bordeaux retook the lead with just minutes remaining.
Tremolinas turned provider again and this time Diabate headed beyond Gregorini with the aid of the crossbar.
There was still time for Faubert to miss a penalty for a fourth but by then the points were already wrapped up for Les Girondins.