Charles Abouo added 16 points and eight rebounds for the Cougars (24-7, 12-4 West Coast), who played without leading scorer Noah Hartsock (knee). BYU clinched the No. 3 seed in next week's WCC tournament and receives a bye to the quarterfinals.
Ryan Nicholas had 19 points and 14 rebounds and Tanner Riley 16 points for the Pilots (6-23, 3-13), who will be the eighth seed. Portland plays No. 9 seed Santa Clara in Wednesday's opening-round contest.
The Cougars scored the game's first eight points and never trailed. The Pilots got within 67-61 with 3:53 remaining but went scoreless for almost two minutes as Abouo hit two free throws and had a three-point play to spark a 9-0 run.
BYU had a decided edge in free throws, making 21 of 31 (67.7 percent). Portland had just nine attempts from the line, making five.