Missy Peterson knocks down a deep 3-pointer to lead Washington to an upset of No. 11 Oregon State. (0:23)

LAS VEGAS -- Missy Peterson wouldn't let Washington's season end.

The sophomore guard hit a deep 3-pointer with 2.3 seconds left to lift the Huskies to a stunning 68-67 upset of No. 11 Oregon State in the Pac-12 Tournament quarterfinals on Friday night.

"When I stepped in I didn't realize how deep I was," said Peterson, who hit two game-winners in high school. "At that point you got to let it fly. When it went in, it was a great feeling."

The victory continued Washington's shocking run as they became the first 11-seed to reach the semifinals since 2012 when Washington State did it. The Huskies knocked off six-seed Utah in the opening round of the tournament. Next up is seventh-ranked Stanford.

"It's pretty awesome to see them achieve the reward of the scoreboard for all their hard work," Washington coach Jody Wynn said. "It's really difficult to win at the Division I level, especially in the greatest conference in the country. We had two coming into this tournament and everyone wrote us off as an easy out."

With the game tied at 65, Peterson inbounded the ball and got it right back five feet behind the 3-point line draining the shot. She fell down raising both fists in the air in excitement as her teammates jumped on her.

The officials reviewed the play and gave a technical foul to Hannah Johnson for coming off the bench with time still on the clock.

Aleah Goodman hit the free throws from the technical foul, but then her final shot from well behind the 3-point line was short at the buzzer setting off a wild celebration from the Huskies.

Amber Melgoza scored 21 points and Peterson had 19 for the Huskies (11-20).

Trailing 55-53 midway through the fourth quarter, Peterson hit consecutive 3-pointers during an 8-0 run that gave Washington its biggest lead of the game. Joanna Grymek got Oregon State within four with 4:10 left. Melgoza hit a floater in the lane to make it 63-57 with just under 2 minutes left.

Oregon State scored six of the next seven points to get within 64-63 after Mikayla Pivec hit two free throws with 19.5 seconds left. Melgoza converted the second of two free throws a second later to make it a two-point game. Pivec answered with a spinning layup with 4.9 seconds left setting up the crazy finish.

"It's not often you see a shot like that go down," Oregon State coach Scott Rueck said. "It's pretty rare. In my career I can't remember if I've been beaten on a 3 like that. ... This one was a gutsy move and a gutsy shot in that situation. I'll have to look at it again. It was somewhat contested, great shot.

This was the second year in a row that Oregon State (24-7) lost as a three-seed in its opening game of the tournament.

The Beavers were up 14 points in the second quarter before Washington scored the final 10 points of the half to close to 37-33 at the break. Darcy Reese, who hit just seven 3-pointers on the season, made four in the first half. She finished the game with 16 points and 10 rebounds.

The Huskies continued that run and took a 51-46 lead late in the third quarter before the Beavers scored the final five points, including a 3-pointer from the top of the key just before the buzzer by Pivic that tied the game, setting up the exciting final quarter.

Pivec finished with 23 points and 11 rebounds for Oregon State (24-7).

BOMBS AWAY: Peterson is 11-for-14 from behind the 3-point line in the tournament. She went five for six from behind the arc against Oregon State. The 13 3-pointers by the team was tied for most in tournament history, matching Oregon and Washington State's mark.

STREAK BUSTERS: Oregon State had won the last seven meetings with Washington. The Huskies' last win was on Feb. 6, 2015.

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