Talia Walton added 19 points and nine rebounds, while Aminah Williams had 11 points and 17 boards, for the fifth-seeded Huskies (20-10), who trailed by as many as 22 in the first half. Washington won despite shooting 32 percent from the floor, including 6 of 31 from 3-point range.
Ariel Thomas led the No. 12 seed Ducks (4-27) with 13 points. Jillian Alleyne scored 11, and she and Liz Brenner grabbed 15 rebounds apiece.
Amanda Delgado's 3-pointer gave Oregon a 35-13 lead midway through the first half. The Ducks were 9 of 15 from 3-point range in the first half.
But Washington, buoyed by a raucous home crowd, rallied to cut that lead to 39-28 at halftime, then kept inching closer in the second half. Kristi Kingma drained a 3-pointer with 8:26 left to give the Huskies their first lead of the night, 53-52.
The Huskies went ahead for good, 61-60, on Walton's jumper with 4:17 to play, and Walton's 3-pointer with 1:13 left gave Washington a six-point lead and effectively clinched the win.
Washington's 22-point comeback was the largest ever in the Pac-12 women's tournament, shattering the previous mark of 16 set in 2004.
Davis, the Pac-12's second-leading scorer, had 19 of her points in the second half. The Huskies needed them against a surprising challenge from an Oregon team that won just two regular-season conference games all season - both against Washington State. The Ducks led for most of the game and stayed within striking distance until the final 2 minutes.
Washington will face No. 4 seed Colorado in Friday's quarterfinals. The Buffaloes beat the Huskies 68-61 in Boulder, Colo., on Feb. 24.