Toulouse end two-decade wait for victory at Clermont
For slumping Clermont, it was an eighth defeat in the Top 14 this season and they are down at 11th in the table.
"I am very satisfied with the performance of my players, the guys attacked from the start and we created a lot of chances," said Toulouse assistant coach Jean Bouilhou.
"We are ending this long series of defeats here. Clermont remains a stronghold of French rugby."
Toulouse ran in four tries, two of them in the first half through winger Juan Cruz Mallia and centre Sofiane Guitoune.
Melvyn Jaminet kicked eight points as the 21-time champions led 18-6 at the interval with Jules Plisson booting two penalties for Clermont.
Jaminet and Paul Graou then turned the screw by adding converted tries early in the second period before lock forward Tomas Lavanini salvaged some pride for Clermont with their only try.
Toulouse ended the game with 13 men after yellow cards for lock Rynhardt Estadt and winger Arthur Retiere.
The dismissals came too late for the home side missing a host of first-choice players.
"This is the first time this season that we have had this feeling of helplessness," admitted Clermont scrum-half and skipper Sebastien Bezy.
"We have taken a huge step back without finding the solutions to erase these mistakes."