Clermont overcame the first-half red card of Julien Bardy to down Castres 19-10 at the Stade Marcel Michelin.
Bardy was sent off on the stroke of half-time for a headbutt on Yannick Caballero but despite playing 40 minutes with 14 men, Clermont were streetwise enough to fight back for the win.
The headbutt came as Caballero was called for coming around the side of a maul, and Clermont flanker Bardy reacted.
It wasn’t clear whether the head connected with Caballero, who made a lot of it, but referee Romain Poite had no hesitation in rightly sending off the Clermont man, with Caballero also given ten minutes in the bin for the repetition of infringements from the visitors.
The visitors led 7-6 at that point after an early try from R