Castres roared back from 17 points down to beat Clermont 31-27 and extend their Top 14 winning run to seven games.
Christophe Urios' men have marched into contention at the end of 2017 and rounded out the year with a stirring comeback victory, which leaves them second in the table.
Morgan Parra kicked 11 points in the first half, with tries from Aurelien Rougerie and Remy Grosso giving Clermont a healthy 21-10 lead at the break, which was extended by two more successful efforts from the tee by Parra in the second half when Castres were down to 14 men with Anthony Jelonch in the sin-bin.
However, Castres scored a pair of tries in the space of four minutes to turn momentum in their favour, before Ludovic Radosavljevic converted his own score with eight minutes to go to set up a grandstand finish.
Maama Vaipulu thought he had completed the turnaround after twisting his way over the line, but the video referee deemed he had not grounded the ball. But Radosavljevic immediately after took advantage of ponderous Clermont defending to pick and run and score the winning try.
Clermont played on way beyond the 80, but wave after wave of yellow shirts crashed into Castres' rock-solid defence, with victory seen out after eight minutes of bruising extra action, in which Radosavljevic was yellow-carded for a cynical, but successful, try-saving obstruction of Nick Abendanon.
Fourteen-man Lyon held firm to see off Pau 35-23 and cling on to the play-off places.
Lionel Beauxis scored 18 first-half points, including a try, as Lyon dominated early on at Stade de Gerland, but Francisco Gomez-Kodela was dismissed on the stroke of half-time for a high hit to threaten the hosts' 10-point advantage.
However, Pau number eight Steffon Armitage saw yellow for obstruction six minutes into the second half, and Lyon took advantage of the even numbers as Thibaut Regard and Liam Gill went over to ensure a first win in six domestic games for the Wolves.