But the Cougars got 20 points and 11 rebounds from Brock Motum and shocked the Bruins 73-61 on Wednesday night.
The win by the last-place Cougars broke a 19-game home losing streak to the Bruins that extended to 1993.
Royce Woolridge added 19 points for Washington State (12-18, 3-14 Pac-12), which also broke a nine-game losing streak that had put coach Ken Bone on the hot seat.
"It's nice to see these guys rewarded with a win," said Bone, whose team has repeatedly lost games in the second half this season. "It's a huge confidence builder."
Jordan Adams scored 18 points for UCLA (22-8, 12-5), which had won four straight games and came into Wednesday tied with Oregon for first place in the Pac-12.
"We didn't come out with the emotion and intensity that we needed," UCLA coach Ben Howland said. "We didn't have the sense of urgency when so much was riding on the line for us."
Shabazz Muhammad added 14 points for UCLA on 4-of-19 shooting.
Washington State had lost its last eight games against the Bruins, who were coming off a win over No. 18 Arizona.
"This is the first time in 19 years we beat them here," Motum said. "I was happy individually to have beaten UCLA for the first time."
Washington State played without Mike Ladd (knee injury) and DaVonte Lacy (knee injury), their second- and third-leading scorers. Bone said Lacy is out for the rest of the season.
It didn't seem to matter, as the Cougars sliced up the Bruins inside for easy layups much of the game.
"We set good screens," Motum said. "Our guys were wide open for baskets."
Washington State, which jumped to a big early lead and never trailed, held the Bruins 15 points below their scoring average, and outrebounded them 46-23. The Bruins shot just 38 percent in the game, compared to 49 percent for WSU.
"For us to have 21 offensive rebounds and them to have 23 total rebounds, that was very impressive," Bone said.
"We showed we can compete with anyone," said WSU's Dexter Kernich-Drew, who had 11 points and 11 rebounds in a rare start because of the injuries.
The Bruins, who also got 10 points from Norman Powell, were outscored 44-20 in the paint, and were 8 of 29 from 3-point range.
"We came out defensively very poor," Howland said. "I did not have my guys ready to play or fearful enough of losing this game."
"They kept getting layups and easy shots," Howland said. "At the other end, we missed some shots early in the game, in the first half, and it snowballed."
Washington State scored the first seven points of the game, and then made four straight layups to build a 15-2 lead. The Bruins made only one of their first 10 shots.
The Bruins did not score their second field goal until there was 10:26 left in the first half and they trailed 19-4.
Washington State extended the lead to 25-4 with 8:28 left. The Cougars made 10 of their first 18 shots.
Muhammad made a 3-pointer to get the Bruins into double figures at 25-12, but Woolridge replied with a 3 for WSU.
Adams scored the last five points of the first half for the Bruins, on two free throws and a 3-pointer, but Washington State led 35-24. The Cougars shot 48 percent in the first while holding UCLA to 30 percent.
Muhammad's 3-pointer cut WSU's lead to 37-31 early in the second. D.J. Shelton scored three straight baskets for WSU to push the lead back to 43-33.
Layups by Woolridge and Motum gave WSU a 56-42 lead with 7 minutes left.
Two 3-pointers helped the Bruins cut WSU's lead to 60-52, but the Cougars made their free throws to stay ahead.
"I thought our guys were good with their composure," Bone said.
D.J. Shelton added 13 points and four assists for the Cougars.
UCLA averages 76 points per game to lead the Pac-12.
The Bruins hold a 102-15 lead in the all-time series.
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