Jayden Hayward's late penalty proved the difference at the Stadio Monigo, pushing Treviso up above Italian rivals Zebre in the table.
But despite the disappointment at the loss, Lam revealed the entire squad were eager to put things right.
He said: "The whole dressing room is pretty gutted, because it's a game that we probably blew. We know we did, from the outcome.
"We're all determined now to get back, recover out of this game, get the whole squad and have a really good week into what is a massive game.
"We have a lot of pride in what we do. That's why we are bitterly disappointed. There's some really good rugby, but there are bits that we are not too happy about. We will have to learn from that.
"It that was our last game of the season, it would be a killer. Now, we have ticked off the box of a semi-final. The home semi-final is not lost if we win next week."
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