Despite failing to get points on the board, Casellato insists his side can be proud of the way they frustrated the hosts for long periods, highlighting the impressive performance of young lock Marco Fuser.
And with Treviso still firmly in contention to also reach Europe's top tier should they finish higher than Italian rivals Zebre, Casellato is confident his side can trouble the visiting Scarlets next Saturday.
"I'm glad we played pretty well against Leinster," he said. "The team especially in defence played a great game, one of the best of the season.
"But in the end we also have regrets because if those two kicks had gone between the posts we would have been under a single point at 60 minutes.
"However we can take confidence ahead of the last game of the season at home against the Scarlets, when we want to and we must do everything to win the points needed to get into the European Champions Cup.
"Marco Fuser's a guy who made an important path this season, growing much in playing time.
"He can become a good second line, not a number five who calls the lineouts but a great number four, who retrieves balls and fights a lot in defence."
Click here to see the best images from Leinster's triumph over Benetton Treviso
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