Abraham Papali’i was sent off for the third time since his debut in August as Connacht’s slim Rainbow Cup hopes died at Stadio Monigo.
The back rower was red-carded for a shoulder to the head in the closing stages as Benetton made it four wins from four and are in control of their own destiny, with Munster now depending on other results to go their way if they are to qualify.
A bad evening for Connacht in Treviso began when Denis Buckley’s 200th appearance lasted just a minute. He had to go off with a knee injury after winning a superb turnover which led to the opening try when Connacht went to the corner and at the second attempt got the drive for hooker Shane Delahunt.
The perfect start was added to when centre Tom Daly converted from the right wing.
But Benetton hit back and got off the mark when centre Ignacio Brex did well to ground the ball one-handed in the right corner despite a tackle from Alex Wootton.
Paolo Garbisi was unable to convert but as the penalties mounted he landed a couple of kicks to lead 11-7 at the break.
Connacht hit the front three minutes after the restart when Paul Boyle finished off a good maul but Garbisi edged Benetton back in front four minutes later with a penalty.
Connacht’s troubles in the scrum led to a yellow card for Finlay Bealham was brought back on at loosehead but the contained the Italians to just a penalty while he was off.
That left Benetton 17-12 in front going into the final quarter and when Papapli’i was sent off Garbisi made the game safe with his fifth penalty. A win over Ospreys in two weeks will guarantee their will be in the final against one of the South African sides in a final which is already pencilled in for Stadio Monigo.