Perpignan were relegated from the Top 14 on Saturday despite picking up a losing bonus-point in Clermont on a drama-filled final day of the regular season.
USAP looked on course to end Clermont's 76-game home unbeaten streak but three yellow cards in the final quarter combined with a miraculous comeback by Oyonnax - who came back from 19-3 down to save a bonus point in Brive - saw the 2009 champions drop out of the top division for the first time in 103 years.
Toulon finished top thanks to a narrow win over Stade FranÃ§ais after Morne Steyn missed a late conversion that would have earned the Parisians a play-off berth.
Montpellier joined Toulon in moving directly into the semi-finals after crushing Racing-Metro 44-10.
Toulouse thrashed Grenoble to leap up the final standings and secure a home play-off.
Clermont 25-22 Perpignan
Bayonne 23-13 Castres
Bordeaux-BÃ¨gles 54-20 Biarritz
Brive 19-17 Oyonnax
Montpellier 44-10 Racing MÃ©tro
Toulon 17-15 Stade FranÃ§ais
Toulouse 38-8 Grenoble
Clermont v Castres (10 May )
Toulouse v Racing (9 May)
Toulon v Toulouse/Racing (16 May)
Montpellier v Clermont/Castres (17 May)
ASM Clermont Auvergne 25-22 USA Perpignan
Parc des Sports Marcel Michelin, Clermont Ferrand
Perpignan came with minutes of saving their place in the Top 14 but buckled under pressure in the dying minutes, punished by three second-half yellow cards.
The Catalans led several times and came close to ending Clermont's four-year winning run at home.
Even a draw would still have been enough to keep the seven-time champions up but a late Morgan Parra penalty gave Clermont a three-point victory. Wales fly-half James Hook will have plenty of regrets having missed a penalty from straight in front of the posts that proved incredibly costly.
Perpignan started badly when Wesley Fofana went over for the hosts. But the Catalans took the lead at 13-10 after Hook converted a try from South African wing Wandile Mjekevu.
But Clermont scrum-half Morgan Para won the kicking battle with Hook, landing a further five penalties to Hook's four.
Pens: Parra 6
Yellow cards: Malzieu, Sivivatu
Pens: Hook 4
Yellow cards: Mjekevu, Guiry, Vilaceca
Clermont:15 Jean Marcellin Buttin, 14 Sitiveni Sivivatu, 13 Aurelien Rougerie, 12 Wesley Fofana, 11 Julien Malzieu, 10 Mike Delany, 9 Morgan Parra, 8 Elvis Vermeulen, 7 Alexandre Lapandry, 6 Gerhard Vosloo, 5 Nathan Hines, 4 Julien Pierre, 3 Davit Zirakashvili, 2 Benoit Cabello, 1 Thomas Domingo.
Replacements: 16 Benjamin Kayser, 17 Vincent Debaty, 18 Jamie Cudmore, 19 Damien Chouly, 20 Ludovic Radosavljevic, 21 Brock James, 22 Regan King, 23 Clement Ric.
Perpignan: 15 Richard Haughton, 14 Wandile Mjekevu, 13 David Marty, 12 Lifeimi Mafi, 11 Watisoni Votu, 10 James Hook, 9 Nicolas Durand, 8 Justin Purll, 7 Alasdair Strokosch, 6 Bertrand Guiry, 5 Romain Taofifenua, 4 Guillaume Vilaceca, 3 Kisi Pulu, 2 Guilhem Guirado, 1 Sebastien Taofifenua.
Replacements: 16 Romain Terrain, 17 Sona Taumalolo, 18 Maxime Delonca, 19 Karl Chateau, 20 Dewaldt Duvenage, 21 Tommaso Benvenuti, 22 Sione Piukala, 23 Giorge Jgenti.
Aviron Bayonnais 23-13 Castres Olympique
Stade Jean Dauger, Bayonne
Castres held onto their play-off spot despite the defeat at Bayonne as Stade Francais's losing bonus-point against Toulon left them a point short of the play-offs.
The champions face a trip to Clermont and the daunting Parc des Sports Marcel Michelin in the play-offs in a repeat of last year's semi-final, in which Castres shocked the odds-on favourites a week after Clermont had lost to Toulon in the European Cup final.
Bayonne led 10-6 at the interval and pressed home their advantage in the second half to finish tenth.
Tries: Ugalde, Rokocoko
Cons: Bustos Moyano 2
Pens: Bustos Moyano 3
Pens: Kockott 2
Bayonne: 15 Scott Spedding, 14 Martin Bustos Moyano, 13 Joe Rokocoko, 12 Matthieu Ugalde, 11 Marvin O'Connor, 10 Santiago Fernandez, 9 Guillaume Rouet, 8 Charles Ollivon, 7 Dwayne Haare, 6 Mark Chisholm, 5 Lisiate Faaoso, 4 Dewald Senekal, 3 Gert Muller, 2 David Roumieu, 1 JC Janse van Rensburg.
Replacements: 16 Anthony Etrillard, 17 Aretz Iguiniz, 18 Opeti Fonua, 19 Jean Monribot, 20 Jean Joseph Marmouyet, 21 Mathieu Belie, 22 Manu Ahotaeiloa, 23 Vitolio Manukula.
Castres: 15 Brice Dulin, 14 Marcel Garvey, 13 Romain Cabannes, 12 Remi Lamerat, 11 Remy Grosso, 10 Remi Tales, 9 Rory Kockott, 8 Antonie Claassen, 7 Ibrahim Diarra, 6 Jan Bornman, 5 Rodrigo Capo Ortega, 4 Christophe Samson, 3 Ramiro Herrera, 2 Brice Mach, 1 Yannick Forestier.
Replacements: 16 Mathieu Bonello, 17 Saimone Taumoepeau, 18 Richie Gray, 19 Yannick Caballero, 20 Cedric Garcia, 21 Daniel Kirkpatrick, 22 Seremaia Bai, 23 Mihaita Lazar.
Montpellier HÃ©rault Rugby 44-10 Racing MÃ©tro 92
Stade Yves Du Manoir, Montpellier
Racing had come into the match as the team with the most points in the second half of the season but imploded as Montpellier ran in five tries to one from Ireland fly-half Jonathan Sexton.
It was one-way traffic as Montpellier led 23-3 at the break thanks to a double from ex-Springbok Wynand Olivier.
FranÃ§ois Trinh-Duc was particularly impressive, scoring a try and finishing with a 100 percent record from the kicking tee for a personal haul of 22 points.
Tries: Olivier 2, Ranger, Trinh-Duc, Combezou
Cons: Trinh-Duc 4, Escande
Pens: Trinh-Duc 3
For Racing MÃ©tro:
Yellow card: Van der Merwe
Montpellier: 15 Pierre Berard, 14 Rene Ranger, 13 Anthony Tuitavake, 12 Wynand Olivier, 11 Yoan Audrin, 10 Francois Trinh-Duc, 9 Jonathan Pelissie, 8 Alex Tulou, 7 Mamuka Gorgodze, 6 Alexandre Bias, 5 Thibault Privat, 4 Robins Tchale-Watchou, 3 Nicolas Mas, 2 Charles Geli, 1 Mikheil Nariashvili.
Replacements: 16 Mickael Ivaldi, 17 Yvan Watremez, 18 Sitaleki Timani, 19 Fulgence Ouedraogo, 20 Eric Escande, 21 Thomas Combezou, 22 Anthony Floch, 23 Paea Fa'anunu.
Racing MÃ©tro: 15 Juan Martin Hernandez, 14 Adrien Plante, 13 Fabrice Estebanez, 12 Jamie Roberts, 11 Marc Andreu, 10 Jonathan Sexton, 9 Maxime Machenaud, 8 Jacques Cronje, 7 Antoine Battut, 6