Five penalties and a conversion from Rory Kockott helped Castres to a 25-20 victory over Toulon at the Stade Pierre-Antoine on Friday.
Castres had the better of the first half and raced into a significant 22-9 lead after 44 minutes thank to Kockott's prolific boot and a try from winger Romain Martial.
Toulon gradually responded throughout the second half thanks to the boot of former England fly-half Jonny Wilkinson, who scored four penalties and a drop goal in total.
Fly-half Remi Tales landed a crucial drop goal to ensure a ten-point margin for the home side, with Matt Giteau's try in the 66th minute bringing Toulon into touching distance but ultimately proving to be not enough.
The win secures Castres position in fourth place in the Top 14, whilst Toulon must wait to see if Clermont can make inroads into their seven-point gap at the top of the table this weekend.
Pens: Kockott 5
Drop Goal: Tales
Pens: Wilkinson 4
Drop Goal: Wilkinson
Yellow Cards: Sheridan, Tillous-Borde
Castres Olympique: 15 Romain Teulet, 14 Romain Martial, 13 Romain Cabannes, 12 Seremaia Bai, 11 Marcel Garvey, 10 Remi Tales, 9 Rory Kockott, 8 Jan Bornman, 7 Piula Faasalele, 6 Ibrahim Diarra, 5 Rodrigo Capo Ortega, 4 Matthias Rolland, 3 Karena Wihongi, 2 Brice Mach, 1 Saimone Taumoepeau.
Replacements: 16 Mathieu Bonello, 17 Yannick Forestier, 18 Benjamin Desroche, 19 Ewert Wessel Jooste, 20 Daniel Kirkpatrick, 21 Remi Lamerat, 22 Pierre Lakafia, 23 Anton Peikrishvili.
Rugby Club Toulonnais: 15 Benjamin Lapeyre, 14 Vincent Martin, 13 Maxime Mermoz, 12 Matt Giteau, 11 Rudi Wulf, 10 Jonny Wilkinson, 9 Sebastien Tillous Borde, 8 Chris Masoe, 7 Steffon Armitage, 6 Joe van Niekerk, 5 Nick Kennedy , 4 Bakkies Botha, 3 Carl Hayman, 2 Sebastien Bruno, 1 Andrew Sheridan.
Replacements: 16 Jean Charles Orioli, 17 Xavier Chiocci, 18 Simon Shaw, 19 Pierrick Gunther, 20 David Smith, 21 Geoffroy Messina, 22 Nicolas Durand, 23 Levan Chilachava.
Referee: Patrick Pechambert