Bernard Jackman's Grenoble bagged eight tries on their way to a comprehensive pre-season victory at the Sportsground.
Connacht were second best after the first quarter and tries from Mahamadou Diaby, James Hart, Fabrice Estebanez, Daniel Kilioni (two), Chris Farrell, Amrand Batlle and Nigel Hunt sealed the win.
Ben Marshall crossed on his debut for the hosts, while Jack Carty and Ian Porter also touched down.
Connacht had all the early possession and it yielded four penalties in the opening six minutes - Carty kicked to the corner every time.
Connacht got their reward in the seventh minute when the fly-half dived over after he evaded the defence that rushed up, but he missed the conversion to the right.
Grenoble found their feet and began to attack a shaky Connacht defence, with Diaby the first profit when he dived over in the 13th minute. Hart missed the conversion.
His opposing scrum-half Porter darted over as Connacht regained the lead but it was short-lived - Hart and Estebanez crossed to give Grenoble an 19-12 interval advantage.
Tries from Kilioni, Farrell and Batlle on the resumption put th game beyond Connacht.
No 8 Fabien Alexandre was yellow-carded and Marshall got over in his absence, but Hunt and Kilioni cancelled that out for a convincing win for the visitors.
Connacht - D Leader; F Carr, A Pewhairangi, B Aki, D Poolman; J Carty, I Porter; JP Cooney, T McCartney, R Ah You; U Dillane, D Qualter; J Muldoon (capt), J Connolly, E McKeon. Reps used: C McKeon, G Naoupu, N Adeolokun, S O'Leary, D McSharry, R Parata, C Blade, F Bealham, S Delahunt, S O'Brien, N White, B Marshall, S O'Brien.
Grenoble - R Caire; A Batlle, F Estebanez, C Farrell, X Mignot; C Gelin, J Hart; F Barcella, L Bouchet, W Demaison; B Hand, J Percival; J Best, M Diaby, F Alexandre. Reps used: D Kilioni, D Coulson, A Hegarty, D Edwards, M Marie, P Kimlin, R Grice, C Loustalot, C McLeod, J Wisniewski, N Hunt J Willison, G Aplon.
Ref - D Phillips (Ireland).