Askia Booker had 18 points and Xavier Johnson added 14 for the Buffaloes (14-2, 3-0 Pac-12), winners of four straight.
"We just did not play Colorado basketball tonight," Buffaloes head coach Tad Boyle said. "We better play better on Sunday."
Dexter Kernich-Drew shot 6-of-8 from long distance en route to a game-best 24 points for the Cougars (7-8, 0-3), while Que Johnson hit the 3-pointer which sent the game into the extra session, finishing with 10 points in all.
"It's hard to lose it gets old, but we played better than we have," Cougars head coach Ken Bone said.
D.J. Shelton's bucket gave Wazzu a 39-31 edge early in the second half, and that proved to be the largest margin for either side until the end of regulation.
Colorado fought back to take a 53-51 edge on two from the line from Johnson with 4:25 left, then Drew-Kernich equalized just under a minute and a half later.
Xavier Talton connected from long range with 1:24 to play and the Buffs led 56-53, but Johnson drained his attempt with six seconds remaining.
A layup from Kernich-Drew gave the home squad a 58-56 edge early in the extra session, but the Buffs fought back to take a 66-60 advantage on Scott's easy bucket with 2:12 to go.
Booker's two free throws gave Colorado a 68-62 margin with 37 seconds showing, yet Shelton and Royce Woolridge sank two from long distance to help pull Washington State within a point.
But Johnson turned the ball over after a Wesley Gordon miss and the Buffaloes held on.
The Cougars led 8-4 early on, but the visitors snapped to attention and Tre'Shaun Fletcher's layup pulled Colorado into a 21-21 tie with 7:23 left in the half capped a brief surge.
Washington State re-established the lead on a Woolridge jumper the next time down the floor and increased that to 34-28 at the break on a Kernich-Drew 3- pointer.
Colorado has won four of its five meetings with Washington State ... Booker was good on 13-of-14 attempts from the charity stripe as the Buffaloes went 26-of-38 on foul shots ... Shelton posted 14 points and a game-best 12 rebounds in defeat.
01/09 02:21:55 ET