LOS ANGELES — Washington State played nearly perfect basketball for the first 19› minutes against Oregon, building a 20-point lead.

It's a good thing, because the Cougars needed almost every bit of that advantage by the time the game was over.

Derrick Low scored 18 points, Taylor Rochestie added 16, and No. 21 Washington State held off the Ducks 75-70 tonight in the quarterfinals of the Pac-10 tournament.

"That's one of the best starts we've had against a talented team," Cougars coach Tony Bennett said. "We needed that cushion at the end."

Kyle Weaver had 14 points and seven assists and Robbie Cowgill added 12 points and six rebounds for the third-seeded Cougars (24-7), who won for the seventh time in nine games following a three-game losing streak.

The Cougars led 42-22 before a basket by Malik Hairston and a 3-pointer by LeKendric Longmire in the final 30 seconds of the first half cut their lead to 15.

The Ducks, who never led, drew within four points on Tajuan Porter's fourth 3-pointer of the game with 1:25 left in the game. But Oregon would get no closer as the Cougars were successful enough at the foul line down the stretch to earn the victory.

"I think the game was lost in the first half," Hairston said. "That's too good of a basketball team to get down that much."

The Cougars advanced to the conference semifinals for the second straight year. Before that, they had a 2-7 record in Pac-10 tournament action.

"I just hope we can add to this by making it past the semis," Low said. "That would make it more special."

The Cougars have put together back-to-back 20-win seasons for the first time in 66 years. They had gone 10 years without a winning season before going 26-8 last year.

Porter scored 17 of his 20 points in the second half, and Hairston had 20 points and seven rebounds for Oregon (18-13), whose final hope for an NCAA tournament berth might have been snuffed out. Maarty Leunen added 11 points and six rebounds for the sixth-seeded Ducks.

Oregon had been the only team that advanced to the semifinals in every Pac-10 tournament since the event resumed in 2002.

"I would have never thought we would have come down here and played a half so poorly," Ducks coach Ernie Kent said. "We played a great second half of basketball. They did enough to close the game out."

Both teams made more than half their shots — Oregon shot 53.2 percent and WSU 52.1 percent. The Ducks committed 13 turnovers to only seven for the Cougars.

Oregon returned four starters from a team that won the Pac-10 tournament last year before reaching the final eight in the NCAA tournament. The Ducks started 8-1 this season, but losses to Nebraska and upstart Oakland (Mich.) at home in December signaled their downfall.

"I'm just going to wait and see what happens," Kent said regarding his team's NCAA tournament hopes.

"I just look around and see that quality of our league," Bennett said. "I would be disappointed if a 9-9 team in this league doesn't get an NCAA tournament bid."

The Ducks won their final three games of the regular season to raise their conference record to 9-9. No Pac-10 team has been invited to the NCAA tournament with less than 10 league wins.

The Cougars had what appeared to be a comfortable 54-37 lead early in the second half, but Porter scored the last 10 points of a 14-4 Oregon run, trimming Washington State's lead to seven points with nine minutes remaining.

The Ducks used a three-point play by Hairston and a Churchill Odia's 3-pointer — his only basket of the game — to draw within five with 4:16 left. The game was in doubt after that until the final 40 seconds.

WSU shot 16-for-26 including 5-for-7 from 3-point range in the first half and committed only two turnovers. Oregon was 10-for-21 including 4-for-11 from beyond the arc with seven turnovers.

Washington State beat Oregon by nine points in each of their regular-season games to end the Ducks' record 13-game winning streak in the series.