Lone Peak (26-3) was the top-ranked team entering the 5A tournament held at Utah Valley University.
But Pleasant Grove (25-6) was seeking a return to the top, where the Vikings were perched after winning three state titles in a row from 2012 to 2014.
"Seventeen-fifteen, fifth set, with the two top teams in the state. It's sad that somebody had to win, somebody had to lose," Lone Peak coach Reed Carlson said. "Of course, I'd rather be on the winning side. Wow, that was awesome."
The two teams swapped victories through the first four sets before heading to the decisive fifth.
In the last set, neither squad had a lead of more than two points.
The first match point opportunity belonged to Pleasant Grove, which led 14-13 before Robinson put away a kill to tie. Lone Peak then had an opportunity at 15-14 when PG's Sara Hamson swung from the middle for a kill.
Jacquelyn Langhaim then got a big block on a shot by Pleasant Grove's Kazna Tarawhiti to put the Knights up 16-15, which then set up Robinson's game-winner.
"I'm proud of my girls. They were resilient. It wasn't our cleanest volleyball, but man they got it done when they needed to," Carlson said.
Lone Peak, led by Robinson's 16 kills and 14 from Gabi Shumway, had a match point in the fourth set.
But Pleasant Grove, paced by Tarawhiti's 20 kills, recovered from a 24-23 deficit by scoring three straight points — the last on a block by Ryenne Robinson — to force the final set.
"I thought we played a great match," said Pleasant Grove coach Allyce Jones, whose team ousted Sky View in an earlier semifinal. "You know, it was one of the most competitive volleyball matches I've ever coached in my life."
For Carlson, a long-time club coach in Utah, the twin five-set victories capped his first season as a high school head coach.
"That's just how we run, I guess," said Carlson of the to-the-limit matches. "It's exciting for the fans and everybody else. They stepped up when they had to. And that team [Pleasant Grove] is awesome, that's all I can say about them."