Toulouse came back from a nine point half-time deficit to edge Treviso 33-21 in Italy on Saturday.
The Heineken Cup giants were put under serious pressure by their Italian hosts, having defeated Leicester in difficult conditions last weekend.
Treviso's Italian international fly-half Kris Burton was their main antagonist, landing seven penalties - six in the first-half - to bolster their reputation as tough opponents on their own track.
Toulouse recovered in the second-half as their pack came into play. Treviso flanker Robert Barbieri was absent in the sin-bin as the visitors pushed over for a penalty try just after the break, with Louis Picamoles carrying several defenders over with him for their second only minutes later.
Vincent Clerc rounded off the scoring and the win with a try on 63 minutes, but Toulouse were unable to find that all-important bonus-point score - losing hooker Christopher Tolofua to a second yellow card at the death.