Irish referee John Lacey gave Evans his first card after nine minutes for a professional foul and then gave him his marching orders for a high tackle on the half-hour.
By that stage Benetton Treviso were 9-3 ahead and a fourth penalty from full back Kris Burton made it 12-3 at the break.
The heavens opened before kick-off and there was water all over the pitch which made life difficult for both sides. Treviso lost two players to the sin-bin, Ignacio Fernandez-Rouyet and Dean Budd, during the game and had to defend for their lives at the death.
But, even though Dan Biggar managed to add a second penalty in the second half, two further misses meant the champions couldn’t close the gap. It left Treviso celebrating their first PRO12 victory over the Ospreys and the Welsh region heading home with a mere losing bonus point.
The victory means that Treviso now only need to beat Cardiff Blues to complete a win over every other team in the PRO 12 in only their third season.
