Roberto Nelson moved into sixth place on Oregon State's career scoring list with 1,473 points in the 66-55 win.
Devon Collier scored 10 points and moved into 11th place with 1,326.
With the victory, the Beavers won in Pullman in consecutive years for the first time in 14 years.
Oregon State built a number of leads that WSU chipped away at, but OSU hit key free throws down the stretch.
"We didn't shoot the ball as well as we normally do, both from the foul line and the outside, but we did enough stuff to win the game," Oregon State coach Craig Robinson said.
Oregon State shot 52 percent from the field, but hit only one 3-pointer in the second half. The Beavers attacked the rim down the stretch and they converted on free throws when it mattered - they were 7 of 8 down the stretch to finish 19 of 27 for the game.
WSU's D.J. Shelton scored a career-high 24 points, going 4 for 4 from behind the arc for Washington State (8-11, 1-6 Pac-12), but the Cougs continued to struggle on the offensive end, in part because of the absence of injured leading scorer DaVonte Lacy. Que Johnson added 15 points against OSU.
The Beavers led by 11 with 6:15 remaining in the game. Cougar threes cut the led to six, 56-50, but that would be as close as the Cougars would get as OSU began converting free throws.
Oregon State built a 10-point lead twice in the first half, including 21-11 at the 9:26 mark. The Beavers shot 69 percent from the field (9 of 13) during the stretch.
The Beavers led 27-17 late in the half but Washington State hit the final two shots to come to within 33-27 but was plagued by turnovers and only hit one free throw, finishing the game 1-4.
The Cougars started the game with six turnovers in the opening eight minutes of play. They started the second half in similar fashion, with turnovers on their first two possessions.
OSU next heads to Seattle to take on the Huskies on Saturday, 2 pm on the Pac-12 Networks.
HOOPS: Oregon State grabs Pac-12 road win
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