Oyonnax stepped closer to Top 14 play-offs on Friday with a 28-10 victory over Lyon, who are now assured of relegation.
The hosts outscored Lyon three tries to one at Stade Charles Mathon, meaning they provisionally move four points clear of sixth-placed Racing Metro and six clear of seventh-placed Montpellier – who both must still play this weekend – with one round of the regular season remaining.
The result also means that last year's ProD2 champions Lyon go straight back down to the second tier of French rugby.
Oyonnax led 18-3 at the interval thanks to tries from wings Silvère Tian and Alaska Taufa. Lyon were hit by the sin binning of South African Coenie Basson after 22 minutes, conceding both first-half tries during that 10-minute period.
Fly-half Benjamin Urdapilleta crossed for the home side's third try from 60m out on the hour mark as he went on to finish the night with personal haul of 18 points.
Former Stormers hooker Deon Fourie's late consolation try wasn't enough to save Lyon, but did deny Oyonnax a vital bonus point.
"Maybe we started with a system which wasn't adapted to the demands of the Top 14," said Lyon coach Olivier Azam, who ironically will coach with Oyonnax next season.
"Maybe we didn't have the players to do it either."
Tries: Tian, Taufa, Urdapilleta
Cons: Urdapilleta 2
Pens: Urdapilleta 3
Yellow card: Missoup
Yellow card: Basson
Oyonnax: 15 Florian Denos, 14 Silvère Tian, 13 Pierre Aguillon, 12 Roimata Hansell Pune, 11 Alaska Taufa, 10 Benjamin Urdapilleta, 9 Fabien Cibray, 8 Viliami Ma'afu, 7 Olivier Missoup, 6 Maurie Fa'asavalu, 5 Damien Lagrange, 4 Thibault Lassalle, 3 Marc Clerc, 2 Jody Jenneker, 1 Antoine Tichit
Replacements: 16 Paula Ngauamo, 17 Ruaan du Preez, 18 Miroslav Nemecek, 19 Valentin Ursache, 20 Yohan Domenech, 21 Hemani Paea, 22 Regis Lespinas, 23 Soane Tonga'uiha
Lyon: 15 Vincent Martin, 14 Toby Arnold, 13 Paul Bonnefond, 12 Thibaut Regard, 11 Mosese Ratuvou, 10 Romain Loursac, 9 Ricky Januarie, 8 Masi Matadigo, 7 George Smith, 6 Steevy Cerqueira, 5 Lionel Nallet, 4 Coenie Basson, 3 Horatiu Pungea, 2 Damien Fitzpatrick, 1 Jeremy Castex
Replacements: 16 Deon Fourie, 17 Francisco Tetaz, 18 Mickaël de Marco, 19 Simon Njewel, 20 Mathieu Lorée, 21 Francois Viljoen, 22 Lachie Munro, 23 Anthony Roux
Referee: Pascal Gauzère