The Cougars (5-3) outscored the Pilots 32-12 in the paint and had a 45-27 rebounding advantage.
Ryan Nicholas had 17 points and hit five 3-pointers for Portland (3-4).
The Pilots trailed 39-33 early in the second half, but Washington State started feeding the posts. Portland had no answer for the inside play of Motum, who scored 17 of his 29 points late in the second half.
Portland shot only 28 percent in the first half, connecting on only 7 of 25 shots.
Washington State shot 42.9 percent (24 of 56) for the game.
Guard Naz Mitrou-Long, whose 2015-16 season ended in December due to hip problems, has been granted a hardship waiver for the coming season, Iowa State said.
As the Sooners look to life without superstar Buddy Hield and his sidekicks, it's clear their unseasoned players will need to grow up fast.
The Central Intercollegiate Athletic Association says it won't move its headquarters, its basketball tournament or other conference championships from North Carolina, despite