The Wales fly-half was stuck in M4 motorway gridlock an hour before the West Walians clashed with Glasgow Warriors at Parc y Scarlets.
But he dusted himself down to steer his region to victory over PRO12 finalists Glasgow, who had only lost once this season before the 19-9 defeat.
Pivac said: “There was some sort of accident on the M4 and Rhys couldn’t get here. It took him two and a half hours to get here from Cardiff so basically he threw his kit on and went straight into the warm-up.
“He felt his knee early on, but played through that and I thought he went very well. He has come back here and been positive.
“He knew he didn’t play as well as he would have liked in the game against Fiji, but he was fine and he wanted to go out and perform well for us and I thought he did that.
“Rhys does a good job for us. He has a big kicking game, gets our backline under way and when he is in a run of form he is as good as anybody around. We are pleased to have him.”
Preistland’s boot was key as the Scarlets used their territorial advantage to keep Glasgow at arms length. No.8 Rory Pitman grabbed a late try to seal the win and Pivac reckons the result to be the catalyst to catapult them into the play-off places.
He said: “We put ourselves under pressure in the week before the Glasgow game. It was a game we said we had to win, and obviously to stay in contention with the top four we needed to do that.
“I thought our set-piece was good. Our scrum and line-out went well too. It is an area we are going to really focus on in this next block with the weather coming in. There are going to be a lot more set-pieces in the game and lot tighter play. We have ground out two wins in the wet in the last two rounds.”
