Biarritz lost their seventeenth match of the Top 14 campaign on Friday as they went down 24-22 to Oyonnax.
The result leaves Biarritz a hefty seventeen points off their opponents, who now trail twelfth-place Perpignan by a further three points in the table.
BO led 8-10 at the break after Charles Gimenez's try and Dimitri Yachvili's conversion and penalty got the better of Benjamin Urdapilleta's points.
An Urdapilleta kick followed by Pierre Aguillon's crossing put Oyonnax in front though before Joe Pietersen replied for Biarritz to make it 18-15.
Urdapilleta extended the visitors' lead up to six points with ten minutes remaining but when Arnaud Heguy scored for the hosts, it was Biarritz now in front 21-22.
But up stepped Urdapilleta in the 78th minute to break Biarritz hearts.
Tries: Gimanez, Pietersen, Heguy
Con: Yachvili, Peyrelongue
Tries: Urdapilleta, Aguillon
Pen: Urdapilleta 4
Biarritz: 15 Joe Pietersen, 14 Taku Ngwenya, 13 Charles Gimenez, 12 Seremaia Burotu, 11 Teddy Thomas, 10 Dan Waenga, 9 Dimitri Yachvili, 8 Imanol Harinordoquoy, 7 Ueleni Fono, 6 Benoît Guyot, 5 Thibault Dubarry, 4 Erik Lund, 3 Francisco Gomez Kodela, 2 Arnaud Heguy, 1 Thomas Synaeghel.
Replacements: 16 Ben Broster, 17 Fabien Barcella, 18 Eugene van Staden, 19 Addison Lockley, 20 Raphaël Lakafia, 21 Yann Lesgourgues, 22 Julien Peyrelongue, 23 Aled Brew.
Oyonnax: 15 Lucas Amorosino, 14 Silvere Tian, 13 Pierre Aguillon, 12 Hemani Paea, 11 Samuela Wara, 10 Benjamin Urdapilleta, 9 Agustin Figuerola, 8 Viliami Maafu, 7 Christophe Andre, 6 Valentin Ursache, 5 Damian Browne, 4 Miroslav Nemecek, 3 Marc Clerc, 2 Salim Tebani, 1 Fiche Lukas Rapant.
Replacements: 16 Neil Clark, 17 Clément Baïocco, 18 Damien Lagrange, 19 Ratu Soqeta, 20 Fabien Cibray, 21 Régis Lespinas, 22 Guillaume Bousses, 23 Antoine Tichit.
Referee: Sébastien Cloute