Brock Motum scored 31 points and Royce Woolridge added 25 as Washington State closed out the regular season by crushing USC 76-51 on Saturday.
Woolridge hit five 3-pointers and Motum three, helping the Cougars (13-18, 4-14 Pac-12) to their first winning streak in conference play this season with a sweep of the Los Angeles schools. Washington State defeated UCLA on Wednesday.
"Considering where we were with our record, to come back home and play two good games does a lot for our confidence, and it was the right time to do it," Washington State coach Ken Bone said. "If we didn't do it this weekend, it would never happen."
The Cougars earned the 11th seed in the conference tournament and plays No. 6 seed Washington on Wednesday in Las Vegas.
T.J. Terrell had 18 points for the Trojans (14-17, 9-9). He was the only player in double figures for USC, as it struggled from the field (19 for 56) and behind the arc (4 for 24).
USC is seeded seventh in the tournament and faces No. 10 seed Utah on Wednesday.
Washington State never trailed and raced to a 22-point lead in the first half. Motum had 21 of his points before halftime.
The Trojans opened up the second half with an 18-4 run and cut the deficit to five, 45-40.
"I thought our guys did a nice job dealing with the run in the second half. They started making shots and pushed the ball in transition," Bone said. "We did not play well the opening minutes of the second half, but we stuck together and started making baskets."
The Cougars put the game out of reach when Woolridge hit four consecutive 3-pointers to make the score 66-46 with 4:42 remaining.
"They have improved a great deal since the last time we played; there is a big difference in how they execute their offense and how they play on defense," USC interim coach Bob Cantu said.
Washington State outrebounded the Trojans 45-34 and committed only five turnovers.