Paris - Castres climbed to third in the French Top 14 on Sunday on the strength of a deserved 29-17 win at Bordeaux-Begles.
The visitors had only scored seven tries on the road all season but that haul reached double figures thanks to first half tries from Horacio Agulla and Anthony Jelonch with Marc-Antoine Rallier crossing after the break.
Julien Dumora, a last minute stand-in for Argentine flyhalf Benjamin Urdapilleta, added 12 points with his boot.
For Bordeaux the defeat stretched their winless run to seven, leaving them ninth, six points shy of the play-off positions.
Despite their two first half tries from Luke Jones and Yann Lesgourgues, Bordeaux lacked bite as Castres controlled the game to boost their chances of appearing in the end of season play-offs for the title.
On Saturday, defending champions Racing 92 put Dan Carter's drink-driving shock behind them with a 33-25 win over Brive as Clermont grabbed pole position after a 46-27 victory over rock-bottom Bayonne.
Clermont's six-try win moved them above La Rochelle who earlier downed Stade Francais 37-18.