Brock James' late introduction was crucial as Clermont beat Toulouse 18-14 to reach the Top 14 final against Stade Français next week.
Often singled out for cracking under pressure, it was the Australian's cool head that proved decisive, slotting a late penalty and drop goal to send Clermont through to the final.
It brings to an end the long reign of Guy Novès at Toulouse, but while the quality seemed to suffer in the scorching conditions, his team gave it their all.
Maxime Médard scored the only try of the match for Toulouse, who led heading into the final ten minutes, but in the end Clermont were able to make their territorial dominance pay.
There were question marks over the Toulouse scrum heading into the game and at the first set-piece they were penalised when the scrum went down, allowing Morgan Parra to open the scoring from just inside the Toulouse half.
Toulouse responded though, at the next scrum as they put Thomas Domingo under pressure, and from out wide Luke McAlister made no mistake. It could have been more for Toulouse, with Yann David stopped just short of the line after a powerful charge.
It was an edgy start and Clermont had their first real period of possession in the Toulouse 22 just before the quarter hour, but Toulouse's defence held before Camille Lopez's drop goal was pulled wide.
They came back again, putting width on the ball to stretch Toulouse, and when Gillian Galan was pinged for hands in the ruck, Parra put Clermont back in front.
Early on it was clear that Clermont were in the ascendancy, regularly creating space out wide and when Yannick Nyanga was slow to roll away from a ruck, Parra stretched the lead to six points.
Jean-Marc Doussain, a surprise inclusion at fly-half for Toulouse, then stepped through a gap in midfield to put Clermont on the back foot, and after a long passage in the 22, they were rewarded with a penalty that McAlister converted to cut the deficit to three points.
That was how it remained until half-time, but Toulouse started the second half the stronger only for McAlister to miss a difficult shot at goal.
They didn't have to wait long to take the lead for the first time though, with Joe Tekori bursting through after a lineout and a couple of phases later Médard went over in the corner, dummying to beat Noa Nakaitaci. McAlister was off-target with the conversion, but Toulouse led 11-9.
Having dominated much of the game, Clermont had failed to take their chances, but they came straight back with Benson Stanley, a constant threat in midfield, cutting through and only just being forced into touch. However a rolling maul was illegally defended by Toulouse a minute later, and Parra took advantage to put Clermont back in front.
Clermont realised the maul was causing Toulouse problems, and they turned to it again in their own half to march Toulouse back 30 metres and strike a psychological blow, even if they couldn't turn it into points.
The heat seemed to be affecting the players, and the game lacked rhythm, but McAlister rediscovered his kicking boots from halfway on the right after Yannick Nyanga had been taken out in the air, putting Toulouse ahead 14-12 with 15 minutes to go.
Clermont were unable to turn possession into points but with nine minutes remaining they got back in front thanks to their scrum. Johnston, back on after youngster Dorian Aldegheri had struggled in the set-piece, was penalised for failing to hold his bind, and James made no mistake.
Les Jaunards knew they had to play the game in Toulouse territory, and James showed all his experience, first driving them into the 22, before slotting an ice-cool drop goal to seal the win.
Toulouse tried to come back, but made too many handling errors to give themselves a chance and Clermont were able to see it out relatively comfortably.
They will now head to Paris to take on Stade Français in a repeat of the 2007 Top 14 final, the last time the Parisians had reached the final.
Pens: Parra 4, James
Drop Goal: James
Pens: McAlister 3
Clermont: 15 Nick Abendanon, 14 Aurélien Rougerie, 13 Benson Stanley, 12 Wesley Fofana, 11 Noa Nakaitaci, 10 Camille Lopez, 9 Morgan Parra, 8 Fritz Lee, 7 Julien Bardy, 6 Damien Chouly (c), 5 Sébastien Vahaamahina, 4 Paul Jedrasiak, 3 Davit Zirakashvili, 2 John Ulugia, 1 Thomas Domingo
Replacements: 16 Benjamin Kayser, 17 Raphaël Chaume, 18 Julien Pierre, 19 Alexandre Lapandry, 20 Ludovic Radosavljevic, 21 Brock James, 22 Jean-Marcellin Buttin, 23 Clément Ric
Toulouse: 15 Maxime Médard, 14 Vincent Clerc, 13 Yann David, 12 Luke McAlister, 11 Yoann Huget, 10 Jean-Marc Doussain, 9 Sébastien Bézy, 8 Gillian Galan, 7 Yannick Nyanga, 6 Thierry Dusautoir (c), 5 Patricio Albacete, 4 Joe Tekori, 3 Census Johnston, 2 Corey Flynn, 1 Gurthö Steenkamp
Replacements: 16 Cyril Baille, 17 Julien Marchand, 18 Yoann Maestri, 19 Louis Picamoles, 20 Yacouba Camara, 21 Florian Fritz, 22 Timoci Matanavou, 23 Dorian Aldegheri
Venue: Nouveau Stade de Bordeaux, Bordeaux
Referee: Alexandre Ruiz
Assistant Referees: Maxime Chalon, Cyril Lafon