Remy Grosso scored a hat-trick for Castres as they beat Clermont 31-10 in Saturday's late Top 14 game at Stade Pierre-Antoine.
The result, Castres' third-straight win, is a massive boost to their hopes of avoiding relegation. It also means that the top three sides in the standings at the start of the weekend were all defeated following Toulon's loss in La Rochelle and Stade Français going down to Toulouse.
The bonus-point wins for Castres and Bayonne this weekend mean that there are just four points between seventh-placed Montpellier and the relegation zone.
A week before their European Champions Cup Final, Clermont sent a much-changed side on the road and they scored the first try after just two minutes via full-back Jean-Marcellin Buttin.
Camille Lopez added the conversion but it was one-way traffic in the other direction for the rest of the game.
Grosso crossed twice with half-time approaching to give the home side a 10-7 lead at the interval.
There was more to come from the hosts, even if Rory Kockott missed four shots at goal.
Former Clermont wing Sitiveni Sivivatu struck early in the second-half to give Castres a healthy lead going into the final quarter, with Clermont's only reply a penalty from Lopez.
Replacement prop Yannick Forestier added a fourth try to seal the win before Grosso bagged his hat-trick with five minutes left on the clock.
Tries: Grosso 3, Sivivatu, Forestier
Cons: Kockott 3
Castres: 15 Geoffrey Palis, 14 Remy Grosso, 13 Thomas Combezou, 12 Rémi Lamerat, 11 Sitiveni Sivivatu, 10 Rémi Tàles, 9 Rory Kockott, 8 Johnnie Beattie, 7 Yannick Caballero, 6 Ibrahim Diarra, 5 Rodrigo Capo Ortega, 4 Christophe Samson, 3 Karem Wihongi, 2 Brice Mach, 1 Mihal Lazar.
Replacements: 16 Mathieu Bonnello, 17 Yannick Forestier, 18 Benjamin Desroche, 19 Jannie Bornman, 20 Lucas Dupont, 21 Julien Dumora, 22 Romain Cabannes, 23 Ramiro Herrera.
Clermont: 15 Jean-Marcellin Buttin, 14 Zac Guildford, 13 Aurélien Rougerie (c), 12 Benson Stanley, 11 Julien Malzieu, 10 Camille Lopez, 9 Morgan Parra, 8 Peceli Yato, 7 Alexandre Lapandry, 6 Julien Kazubek, 5 Julien Pierre, 4 Loïc Jacquet, 3 Clément Ric, 2 John Ulugia, 1 Raphaël Chaume.
Replacements: 16 Ti'i Paulo, 17 Thomas Domingo, 18 Paul Jedrasiak, 19 Damien Chouly, 20 Ludovic Radosavljevic, 21 Mike Delany, 22 Noa Nakaitaci, 23 Michael Simutoga.
Referee: Christophe Berdos