Agen used to reach the knock-out stages of Europe on a regular basis and, while they have not done so since 2005, they took the first albeit tentative step in putting that right with a 36-31 Pool 4 victory on the road at the Peroni Stadium.
After a three-year absence from European competition Calvisano struck first when flanker Giacomo Broncoli went over for a try after just two minutes, former Azzurri scrum-half Paul Griffen converting and adding a penalty to remind Agen they had some work to do.
And they promptly got to work with a try by Leo Bastien converted by Raphael Lagarde before taking a lead they never surrendered with right wing Leka Tagotago securing the try bonus point just a minute after the break.
Scrum-half Sylvain Dupuy and No8 Uelenitoni Fona had already breached the Calvisano defence for a 31-17 half-time advantage but Calvisano showed tremendous spirit by staging a great comeback with lock Jaco Erasmus to the fore that earned them both try and losing bonus points and had Agen hanging on for victory.