The Pilots (4-0) will play No. 22 Minnesota in the semifinals Friday.
Portland, coming off a seven-point win over Oregon, never trailed. It was UCLA's largest margin of defeat since losing 79-48 at Oregon on March 1, 2003.
The Pilots, picked second in the West Coast Conference preseason coaches poll, knifed through UCLA's defense with ease, scoring off the dribble and making 3-pointers.
Entering the game having made 52.1 percent of their 3-point attempts, the Pilots continued making a barrage of long-distance shots to bury the Bruins. Portland sank 11 of 19 3-pointers and shot 54.2 percent overall.
Conversely, UCLA shot 32.7 percent overall and 21.7 percent on 3-pointers. The Bruins converted just 6 of 14 free throws.
The 47 points were the fewest UCLA had scored since a 55-48 loss to Washington State on Feb. 5, 2004.
UCLA was so inept on both ends of the court that a fan sitting across from the Portland bench yelled late in the second half, "Come on, you're embarrassing us!" and, "Come on, have some pride! Let's go!"
Stohl made all five of his 3-point attempts to move up to third on the Pilots' career list for 3-point baskets, while Nik Raivio contributed 13 points and five assists.
UCLA forward Nikola Dragovic rejoined the team after serving a two-game suspension. Dragovic, who finished with three points, was suspended after he was arrested in an assault case. He was reinstated Tuesday.
The Pilots made 6 of 8 3-pointers and shot 57.1 percent from the field en route to a 36-19 halftime lead.