The loss dropped the Beavers (18-5, 8-4) into third place behind Arizona (9-3), which beat front-running USC, 60-55. Washington (18-8, 9-5) is in fourth place.
The victory was only the second at Corvallis for Washington Coach Marv Harshman, the last coming in 1977.
Oregon State went into the game leading the conference in shooting for the season (54%) but could connect on only 11 of 48 attempts for 23%, including 4 of 23 in the first half.
Detlef Schrempf led Washington scorers with 22 points. Chris Welp added 18 before fouling out with 4:22 left.
A.C. Green was high scorer for the Beavers with 19 points, including 11 free throws. He also pulled down a game-high 14 rebounds.
A 10-1 scoring run by the Huskies gave them a 12-7 lead eight minutes into the game and they never trailed after that.
Stanford (10-12, 2-10) led by as many as nine points in the second half, and had a 39-38 advantage with 10 seconds to go. But a free throw by Cal's Chris Washington sent the game into overtime.
Johnson gave Cal (12-10, 4-8) a 41-39 lead with a minute gone in the first overtime, but two free throws by Stanford's Kent Seymour with 37 seconds remaining tied the game and forced a second extra period.
Greg Butler was high scorer for the Cardinal with eight points.
Washington State sophomore forward Joe Wallace had a game- and career-high 33 points. But he missed a key shot with four seconds to play that could have tied the game at 84.
Oregon is 5-7 in the Pac-10, 12-13 overall. Washington State is 3-10 in conference, 11-12 overall.