Leigh Halfpenny contributed 21 points as Toulon kept their Top 14 title hopes alive in dramatic fashion on Friday, beating Castres 26-22 at Stade Mayol despite losing two players to yellow cards in the second half.
When Drew Mitchell followed Liam Gill into the sin bin for a deliberate knock-on, which resulted in Castres being awarded a penalty try, Toulon were briefly down to 13 men and faced a six-point deficit with 24 minutes remaining.
However, the third of four Halfpenny penalties reduced the hosts' arrears just as Gill returned to the fray and the Wales full-back then went over in the left corner to put his side back in front, with Castres still boasting a numerical advantage.
Halfpenny converted his own try and added another three-pointer, before Toulon - last year's runners-up - survived a late rally from their opponents to book a semi-final tie against La Rochelle.
With the exception of the penalty try awarded following Mitchell's infringement, all of Castres' points came from the trusty left boot of Benjamin Urdapilleta.
Although the visiting fly-half landed three penalties to Halfpenny's two prior to the interval, Toulon led at half-time thanks to a try from Laurent Delboulbes that was set up by Francois Trinh-Duc.
Thomas Combezou was denied a try by the TMO early in the second period, but Castres were nevertheless able to get back within a point, Urdapilleta making no mistake after Gill had been yellow carded for a high shot on Rory Kockott.
The retiring Mitchell - in what would have been the final game of his career had Toulon lost - was soon sin binned as well, leaving Castres as strong favourites.
Yet Toulon responded superbly and Halfpenny's fine finish in the left corner, after classy set-up play from Mathieu Bastareaud and Ma'a Nonu, ultimately decided the game.