Another big loss for Grenoble
Grenoble fell to their second big defeat in succession when they were beaten 38-8 away to Toulon at the weekend.
The European champions ran in six tries to Grenoble's one, having led 14-0 at the break with Ma'a Nonu and Daniel Vermeulen scoring the first-half tries.
Former Clontarf scrum-half James Hart, who has been linked with a summer move to Ronan O'Gara's Racing 92, pulled back a penalty for Grenoble after the restart.
But the reprieve was short-lived, with Delon Armitage crossing after 50 minutes and Drew Mitchell going over for the first of his brace less than a minute later.
Grenoble, who had been blitzed the previous week when Clermont hit them for 21 points in the opening nine minutes on their way to a 45-12 triumph, must have feared a similar hiding.
Juan Smith got Toulon's fifth try with 22 minutes remaining on the clock to make it 31-3.
But Grenoble only conceded one more try in the final quarter, with Mitchell getting his second of the game to keep them third, two points off leaders Racing 92 with Clermont in between them.
Grenoble had the final say with a try three minutes from time when winger Lucas Dupont scored.
There is no action in the Top 14 this weekend and Grenoble will be glad of the chance to regroup before they host La Rochelle next weekend