Scarlets remain top of the GUINNESS PRO12 table after 13 matches, though they are now level on points with Connacht and just four clear of sixth-placed Munster.
And Pivac has told his team they cannot afford any more slip-ups if they are to finish inside the top four.
"The next game is hugely important," he said. "It's a home game and one we have to win.
"We've spoken already this season about how close this competition is and Saturday's result, and when you throw yellow cards into the mix, it hasn't made things any easier for us.
"After a disappointing first half where the scrum struggled against a very strong Connacht pack we were pleased to see us starting well in the second half and the boys doing exactly what we'd asked of them.
"With only three points in it and the conditions in our favour we were confident that we were back in the game.
"The turning point was the knock-on from the restart and the penalties that quickly followed. We'll keep battling on, we probably can't rotate the squad as much as we'd like."
To buy tickets for the GUINNESS PRO12 Grand Final click here. Also follow us on Facebook, join the conversation on Twitter, sign up to our YouTube channel for extensive match highlights and sign up for our newsletter for regular updates on the GUINNESS PRO12.