How big was the Eagles' comeback? Fifth-ranked Intermountain, which had defeated Duchesne in four sets earlier in the season, led 13-7 in the fifth.
But behind the serve of senior Kaylie Grant, the Eagles' only senior, Duchesne reeled off seven straight points.
A kill by Audrey Green, Intermountain's leader with 31 putaways, tied the fifth set at 14-14. That's when Spencer got her 15th kill of the night to bring a second match point for Duchesne - which she finished herself with a service ace.
After the win, Eagles' coach Eric Jessen said he had to force himself to stay seated on the bench and let his young players work through their trouble spots.
"It's a real interesting group — it's a group I cannot yell at, because they'll go cry on me," said Jessen, while checking his fitness wrist device for his heart rate. "I have to sit and let them play through it."
Quite the opposite, from an experience standpoint, was Intermountain. The Lions had seven seniors in Friday's match and staged their own comeback after losing the first two sets and trailing 22-20 in the third.
"It was definitely one of the crazier matches we've played," Intermountain Christian coach Brenna Blackburn said. "Part of it was they were looking too far forward in the tournament and then realizing that we've got to play this match and get our heads into the game."
Duchesne will play two-time defending champion Panguitch in a semifinal today as the top-ranked Bobcats breezed by Altamont 25-14, 25-19, 25-23 in a quarterfinal match.
Rich also worked its way into the semis, overcoming a bad start to beat St. Joseph 23-25, 25-14, 25-16, 25-16.
Awaiting the Rebels is second-ranked Monticello as the Buckaroos blew out Milford 25-18, 25-12, 25-12 in another quarterfinal.
Monticello coach Tony Esplin is trying to get his team back in the winner's circle for the first time since the back-to-back championships of 2011 and 2012.
"This is a pretty special group, very talented," said Esplin, whose team was paced by seniors Atlanta Black and Izabell Slade in the middle. "Several of these girls have been starting for a couple of years. They've had some upsets that still haunt them, but they pull together really tight and, right now, they're playing with confidence."