Tries by front-rowers Kristian Dacey and Sam Hobbs decided the game at a windy Cardiff Arms Park, with outside-half Gareth Davies adding the rest of the points with the boot as Treviso lacked a cutting edge.
Conditions were blustery in the extreme, the posts moving violently in the wind to make life difficult for the kickers. It was also swirling, but the strongest wind seemed to be behind Treviso in the first half.
That forced the Blues to keep ball in hand and their adventure paid off when they ran from deep, with a kick ahead from full-back Dan Fish bringing an attacking scrum five metres from the Treviso line.
The Blues attacked from the perfect position and were able to work hooker Kristian Dacey clear on the right to score the opening try. Outside-half Gareth Davies, a match-winning hero against Toulon, was able to land the conversion to add to an earlier penalty.
Treviso's Mat Berquist was happy to go for goal from long range. He was successful from just under 50 metres, pushed one wide from just a little further out and then added his second from close range and in front to narrow the gap.
The visitors then took the lead when quick passing opened up space for outside centre Michele Campagnaro to scamper clear, getting closer to the posts to make the conversion easy for Berquist.
Treviso thought they had scored just before half-time only to be denied by a knock-on, but still went in 13-10 ahead at the break.
It was the turn of the Blues to press with wind at their backs in the second half.
Flanker Andries Pretorius was denied a try in the corner by a forward pass.
Howver they were soon back in front, full-back Dan Fish taking a kick at pace to set up a try for prop Sam Hobbs, converted by Davies.
The heavens opened, but on the artificial pitch at the Arms Park both sides were able to keep playing attractive rugby. The Blues missed two chances to extend their lead as Davies pushed penalties either side of the posts.