Oregon State (19-4, 12-2 in the Pac-10) handed Washington State (7-18, 1-14) its 14th consecutive loss, a school record.
The Beavers held a 17-point lead when Payton took a breather with 1:25 left in the first half. The margin stretched to 77-55 with 3:13 left in the game.
Payton, who had 11 assists, teamed with Earl Martin, who scored 17 of his 22 points in the first half, as the Beavers took a 49-35 halftime lead.
The Cougars took a 7-3 lead, but Payton's basket tied it, 7-7, at 17:03 and the Beavers never trailed again.
Payton's five steals helped keep the Cougars off balance, halting several comeback attempts.
Scott Haskin collected 16 points and eight rebounds for the Beavers, and Allan Celestine added 11 points for the Beavers.
Darryl Woods scored 18 points for Washington State, Brian Paine added 14 and Bennie Seltzer had 10. Woods and Paine each grabbed eight rebounds.
The Beavers made 31 of 58 shots and sank 16 of 20 free throws. Washington State managed only 21 of 52 shots and 16 of 23 free throws.