The Cougars (14-13, 6-9 Pac-12) jumped to a 10-0 lead and held the Sun Devils to single digits throughout the first half, leading 36-8 at the break. The eight points represent the fewest allowed by WSU in a first half since the shot clock was introduced 25 years ago.
In the first half, the Sun Devils shot 17 percent from the floor and were 1 of 6 from beyond the arc. The Cougars shot 48 percent and were 6 of 14 from behind the 3-point line.
"The key was our defense," Washington State coach Ken Bone said. "I thought our guys just locked in mentally."
The Cougars not only scored the first 10 points of the half, but the last 15. While ASU as a team only had eight points, Lacy, a freshman, scored 14 before the break. Motum matched the Sun Devils with eight first-half points.
"Tonight our starters blew them out of the water and then we maintained our lead," Motum said. "We didn't do a good job early (in the second half). Sometimes it's hard in those games to not be complacent, but we did a good job finishing them off."
Arizona State (8-19, 4-11) went to a full-court press in the second half and nearly got back in the game. The Sun Devils put together a 23-7 run and pulled within 43-31 with 13:07 left. But WSU's Dexter Kernich-Drew made a 3-pointer and was fouled and made the free throw for his only four points of the game and the Cougars stayed in control.
"I figured they (Sun Devils) are not going to play the second half like they did in the first half, and that 23-7 run was a disappointment," Bone said. "But we came back and made some plays in transition."
Marcus Capers was a key player in breaking the press, finishing with nine points, 10 rebounds and seven assists for Washington State.
"That 2-3 zone is very good, but Marcus was in the right spot at the right time and made good plays," Bone said. "He did a great job of finding the open area in that zone. He had a very good presence on the floor."
The Sun Devils' Chris Colvin led all scorers with 18 points. Arizona State finished at 38 percent for the game after only making three field goals in the first half. The Cougars shot 47 percent on Saturday.
It was Arizona State's final road game of the season. The Sun Devils, who went 2-8 on the road, finish the Pac-12 regular season with games at home against UCLA, USC and Arizona.
Washington State finishes its home season next weekend against Washington, followed by road games at UCLA and USC before the Pac-12 tournament.
The teams met last month in Tempe, Ariz., with Arizona State winning 71-67. But the Sun Devils have lost five of six since. Washington State also had been struggling before Saturday.
"It's nice to win," Bone said. "We lost three of four to three very good teams, and we needed a win to keep our confidence."