Bayonne moved well clear of the Top 14 relegation zone on Thursday thanks to a 22-12 win over Castres at Stade Jean Dauger.
A first-half try from centre Gabiriele Lovobalavu and five penalties via the boot of fly-half Jacques-Louis Potgieter proved enough for the Basques hosts, who remain eleventh in the league standings but now enjoy a twelve-point cushion on the relegation dogfight.
For Castres, a fifth consecutive defeat in all competitions is an unwelcome result after their elimination from the Heineken Cup last weekend.
The bad news does not end there for les Tarnais who look set for a long spell without lock Joe Tekori after he was forced off with a suspected broken wrist.
The turning point of the game came on the half-hour mark, with Castres on full attack. But a loose ball at a ruck allowed Bayonne to kick and chase, forcing Castres full-back Brice Dulin into a mistake. Bayonne full-back Scott Spedding played it quickly and found the charging Lovobalavu, who crashed over in the corner.
Potgieter added the extras to give the hosts 13-6 lead which turned into 16-9 by half time.
The second period proved and evenly-matched affair with Potgieter and fellow South African Rory Kockott trading penalties.
But it would be Bayonne who finished the stronger, denying Castres a losing bonus point in the dying minutes.
Pens: Potgieter 5
Pens: Kockott 4
Yellow card: Samson
Bayonne: 15 Scott Spedding, 14 Sam Gerber, 13 Joe Rokocoko, 12 Gabiriele Lovobalavu, 11 Marvin O'Connor, 10 Jacques-Louis Potgieter, 9 Mike Phillips, 8 Dwayne Haare, 7 Julien Puricelli, 6 Jean Joseph Marmouyet, 5 Mark David Chisholm, 4 Dewald Senekal, 3 Nemiah Tialata, 2 David Roumieu, 1 Aretz Iguiniz.
Replacements: 16 Gregory Arganese, 17 Pierre Lafond, 18 Abdellatif Boutaty, 19 Marc Baget Rabarou, 20 Cedric Garcia, 21 Benjamin Boyet, 22 Thibault Lacroix, 23 Renaud Boyoud.
Castres: 15 Brice Dulin, 14 Romain Martial, 13 Romain Cabannes, 12 Remi Lamerat, 11 Marc Andreu, 10 Remi Tales, 9 Rory Kockott, 8 Antonie Claassen, 7 Yannick Caballero, 6 Jan de Bruin Bornman, 5 Iosefa Tekori, 4 Matthias Rolland, 3 Anton Peikrishvili, 2 Brice Mach, 1 Yannick Forestier.
Replacements: 16 Marc Antoine Rallier, 17 Michael Coetzee, 18 Christophe Samson, 19 Piula Faasalele, 20 Thierry Lacrampe, 21 Daniel Kirkpatrick, 22 Marcel Garvey, 23 Mihaita Lazar.
Venue: Stade Jean Dauger, Bayonne
Referee: Pascal Gaüzere