"We've always expected a lot from ourselves," Cal coach Joanne Boyle said.
But it wasn't easy, as it took two overtimes for the No. 22 Golden Bears to beat the Beavers, 67-61 Saturday night.
Cal (20-7, 10-6 Pacific-10) earned its first 20-win season since the 1991-92 team finished 20-9.
"It's a great reward, and humbling in a way, that we have won 20 with a couple of games left," Boyle said.
Devanei Hampton's layup and a pair of free throws from Ashley Walker put the Golden Bears up 64-61 midway through the second overtime.
Walker's layup with 50.1 seconds left gave Cal a 66-61 lead to seal it. Hampton had 17 points and eight rebounds and Walker finished with 16 points and eight rebounds.
"I had a trust in my teammates," Walker said.
Ashley Allen's 3-pointer with 2:29 left gave the Beavers a 52-50 lead in regulation, but Hampton's short jumper with under a minute left tied it at 52.
Oregon State's defense kept Cal from getting a shot off, and a shot-clock violation gave the Beavers the ball with 8.3 seconds left. Allen's long jumper fell short before regulation expired.
Both teams struggled offensively in the first overtime. But the Beavers went up 55-54 on Judie Lomax's hard-fought layup and free throw. Casey Nash added a pair of free throws to make it 57-54 with 1:06 left.
Keanna Levy's layup narrowed it to 57-56 for the Bears. Oregon State's Mercedes Fox-Griffin missed one of a pair of free throws with 24.3 seconds left that would have given Cal a 3-point deficit.
Walker made a layup with 4.5 seconds left that tied it again at 58. Fox-Griffin drove the ball down the length of the court but couldn't get a shot off in time, and the game went into its second overtime.
It was the seventh straight loss for the Beavers (8-17, 3-13), who were coming off a 70-55 loss to No. 9 Stanford on Thursday.
Nash, playing in her final home game at Oregon State, scored 25 points. She was held to a lone basket in the second overtime.
"They grabbed her. They held her, and they played her physical _ and there were no calls," Oregon State coach LaVonda Walker said, before turning to Nash.
"Was that right?" Walker asked Nash, who nodded.
Cal, which lost 62-42 at Oregon on Thursday, has lost two of its last four.
Cal led the entire first half, but struggled down the stretch against Nash, who hit a 3-pointer to narrow it to 23-22 for the Beavers. After Hampton's jumper for Cal, Nash scored on a layup and hit a jumper at the buzzer to give Oregon State a 26-25 lead at the half.
Nash led all players with 15 points in the first half.
Julie Futch hit a 3-pointer early in the second half that put the Beavers up 32-27.
Levy's 3-pointer from the corner narrowed it to 41-40 before Natasha Vital's jumper put Cal back in front.
The two teams traded the lead down to the final minutes.
"We came out and we fought hard and had a couple of different chances at it and couldn't close it out," Nash said.
The Golden Bears downed Oregon State 63-57 last month in Berkeley. Cal has won six of the last seven over the Beavers.
It was only the second double-overtime game in Oregon State's history. The last was in 1981.