PARIS - A late try by Oyonnax's Jonathan Bousquet gave his side a losing bonus point that kept them in French Top 14 rugby and sent Perpignan down for the first time in 103 years.
With Bayonne winning comfortably 23-13 against champions Castres it came down to a straight fight between Perpignan and Oyonnax for survival.
The Catalans led several times and came close to ending Clermont's four-year winning run at home, which now extends to 75 matches, before succumbing 25-22.
That bonus point defeat would still have been enough to keep the 2009 champions in the Top 14.
But Oyonnax came back from 19-3 down at Brive, who had nothing left to play for, to score tries from Guillaume Bousses in the 66th minute and then Bousquet eight minutes from time to lose only 19-17 and secure themselves a bonus point.
Seven-time champions Perpignan had never before been relegated from the top flight in the professional era and had not gone down since 1911.