Meantime, UA pitcher Becky Lemke scattered four hits and kept Cal off balance throughout the game. Lemke (29-7) struck out seven including the side in the seventh, while Forest (23-7) struck out nine. The game was 16 batters old before the first hit -- a liner to right by Cal shortstop Katie May.
Lauren Bauer's baserunning staked Arizona to a 1-0 lead in the third. She doubled over the head of Cal centerfielder Amber Phillips with two outs, then kept going and slid under the tag at home on the next play when Toni Mascarenas beat out a single to deep short.
Collins' eighth home run of the year, a solo blast to left, extended UA's lead to 2-0.
Collins' ninth of the season, almost to the same spot in left, came in the bottom of the sixth.
Cal's best chance for a run came in the fourth, but it left runners at second and third. Maiko Bristow led off with a single, Lisa Iancin was hit by a pitch and both runners moved up on Megumi Takasaki's sacrifice bunt. Lemke got two ground outs to end the threat.
Arizona, too, stranded runners at second and third. In the first inning Nicole Giordano and Bauer walked and were sacrificied to third by Mascarenas, but Forest struck out Jennie Finch and Felecity Williams.
The game was played before a crowd of 2,401 at ASA Hall of Fame Stadium. Arizona moves into a winner's bracket game Friday at 8:30 p.m. against Washington, an earlier winner over Arizona State. The Bears will play ASU on Saturday at 2:30 p.m.