Diamond's side were subjected to a tense finish as spirited Treviso poured forward in search of the winning score.
"We will have to play at 100 per cent for 80 minutes to stand a chance against Biarritz. Biarritz is a very hard place to go," Diamond said.
"But this result has helped our confidence and we're confident that when we go down there we will give it the best shot we can."
Dan Scarbrough, Dan Harris, Kevin Yates and Mark BartholomeuszÂ touched down but man-of-the-match Marius Goosen, who finished with 22 points, gave Treviso hope.
Treviso coach Craig Green was delighted by his side's battling performance and warned Saracens of the challenge they face in Biarritz.
"We were a little bit unlucky at the end. I was very happy with the way the guys played throughout the 80 minutes. We came back well in the second half," he said.
"Saracens will have to play a lot better than that against Biarritz but anything can happen in a game like that. Biarritz are a class act and have a lot of Heineken Cup experience."
Sale director of rugby Philippe Saint-Andre insisted his side had achieved their target for the season after qualifying for the quarter-finals with a 30-10 win over Newport-Gwent Dragons.
The Sharks made it five wins out of five in this season's competition by completing a bonus-point victory over the patched-up Welsh outfit.
Mark Cueto (two), Sebastien Chabal and 15-point Charlie Hodgson grabbed Sale's tries.
Saint-Andre said: "Our target at the beginning of the season was to qualify for the quarter-finals of the Heineken Cup and with this win, and four tries, we are sure to be at least one of the best-placed runners-up."
"It's one step but if we want to finish top of our group we need to be much, much better next week at Munster.
"We did the job of scoring four tries. We did enough, nothing more."
Dragons head coach Paul Turner, a former Sale player-coach and a man regarded as one of the founders of the current Sharks empire, was proud of his side's efforts.
"It was always going to be a difficult task against one of the best sides in England and we started off poorly," he said.
"But the longer the game went on, the more of it we had and we went toe to toe with them."