Clermont snapped Grenoble's home-winning streak of 25 games with a hard-fought 17-10 victory in Top 14 action on Saturday.
Despite missing a host of players away on international duty for the Six Nations, Clermont's visit nonetheless attracted a 20,000-strong crowd in cold, snowy conditions.
Clermont, themselves also holders of an admirable home record, scored two tries either side of half-time through wingers Napolioni Nalaga and former All Black Sitiveni Sivivatu, fly-half David Skrela converting both and hitting a penalty.
Grenoble's sole try came from replacement Jonathan Pelissie, his five-pointer too late in the game to change the outcome.
The result left Clermont just three points adrift of leaders Toulon, who lost 25-20 to Castres on Friday, and sees Grenoble sitting three points off sixth place, with the top six going through to the end-of-season play-offs.
Toulouse consolidated their third spot with a convincing 42-6 win at home over Bayonne.
Fifth-placed Montpellier sealed what could be a crucial 15-13 victory over Bordeaux-Begles, while Racing-Metro also notched up a valuable 23-11 win over Biarritz.
Bottom-placed Mont-de-Marsan went down 9-3 away to Agen.