Herriman (23-9) jumped to a 5-0 lead when Micaela Thomson started the proceedings in the first with a long drive over the right-center fence for a two-run homer.
Libby Parkinson delivered the next punch when she doubled with the bases loaded in the third.
But momentum shifted in the fourth. West's Keisha White hit an opposite-field triple to right to start the inning, and the Panthers scored three. West tallied six more runs to surge ahead in the fifth.
White said she thought the team's late-season slump, which saw the Panthers drop from the No. 1 ranking and relinquish the region title as well, might turn out to be a positive.
"I think we needed a couple of losses because we've been so high these last two seasons," White said. "I think winning all those games put us in a big-head mode. In the long run, I think the losses will make us better."
The Panthers scored three more in the seventh, including a home run by Huntyr Ava, for a 13-7 lead.
It was far from over.
Shalee Jensen tripled to kickstart the Herriman rally in the seventh.
West pitcher Macayla Ulibarri, who left the game with one out, re-entered two batters later to face Krystal Kemp with the tying runners in scoring position.
Kemp singled to score one, but the second runner was cut down at the plate on a solid throw from the outfield. Ulibarri struck out Parkinson to end the game.
Herriman coach Heidi McKissick lamented a drive by Kemp moments before her single that went down the right-field line and appeared to clear the bases. But the drive was ruled to be a foul ball.
"I thought it was fair. It would have been an inside-the-park home run," McKissick said.
West 13, Herriman 12
• West dodges the consolation bracket of the 5A draw with its second one-run victory of the season at Herriman.
• West sophomore Huntyr Ava hits a seventh-inning home run in the seventh while Herriman's Micaela Thomson scorches a fence-clearing shot in the first.
• Macayla Ulibarri pitches to all but two batters for West, exiting and re-entering the game in the seventh to get the win and the save.