Megan Langenfeld hit a walk-off homer in the eight to give UCLA a 6-5 win and a 1-0 series led in the championship series.
Harrison's clutch hit with two out in the sixth clipped the outside of the left-field foul line and put UCLA up 4-2, but that was only the start of the drama.
Arizona answered with back-to-back homers by K'Lee Arredondo and Stacie Chambers to go ahead in the seventh. Arredondo's opposite-field drive just cleared the wall in left-center for a two-run shot. Chambers then blasted a mammoth drive that ricocheted off an elevated camera positioned beyond the bleachers in center.
Just when the 10th-seeded Wildcats looked as if they were going to win, they found a way to let UCLA back in it.
Brittany Lastrapes and Lauren Schutzler swerved to avoid a collision on Dani Yudin's potential game-ending fly ball to left-center, allowing it to fall between them for a double. After Julie Burney—who hit the winning homer in one of the teams' regular season meetings—was intentionally walked, Kaila Shull tied it at 5 with an RBI double off Karissa Buchanan's outstretched glove at the track in right.
Then Langenfeld, who gave up the back-to-back homers before being replaced by Aleah Macon (12-1), came up with the biggest hit of all. She pumped her right fist in the air twice after rounding first and was mobbed by her teammates when she made it to home plate.
The Bruins are seeking their 11th NCAA title, not counting the one that was vacated, but their first under coach Kelly Inouye-Perez. She won three championships as a catcher for UCLA.
The Wildcats have won four of their previous six meetings in the finals, with one of UCLA's wins coming in the 1995 championship that's been erased from the record books. The last meeting came in 2001, when the championship was still decided in a single game.