Alex Wintering led all scorers with 26 points for the Pilots (5-7).
Weber State led 35-26 at the half before pushing the lead to as many as 12 points. But Portland closed the gap and took a 61-60 lead with 5:09 left in regulation on D'Marques Tyson's 3-pointer.
Knotted at 69, Taylor Gabe hit a layup with 41 seconds to give Portland the lead. But Senglin's 3-pointer at the buzzer tied the game at 73 and sent it into overtime.
Jazz Johnson's 3-pointer gave the Pilots at 78-75 lead in the extra period, before Senglin again came through with a 3 and Kyndahl Hill dunked to give Weber State an 84-78 advantage. The Wildcats led the rest of the way.
Weber State has won all nine games it has played against Portland.
It was the opening game of the Far West Classic at Portland's Moda Center, home of the Trail Blazers. Cal State Fullerton played Oregon State in the late game Friday night. The Pilots also play Cal State Fullerton on Saturday night.
Weber State took a 26-17 lead in the first half on Zach Braxton's layup, but Portland came as close as 28-26 on Jarrell Marshalls' jumper and free throw. The Wildcats answered with a 7-0 run to push the lead to 35-26.
Bolomboy's layup with 12:34 to go in the game made it 53-41.
Portland closed within six points midway through the half, then capitalized on a 15-6 run capped by Tyson's pull-ahead 3-pointer.
The Far West Classic used to be one of the premier holiday basketball tournaments on the West Coast before its demise 19 years ago. The eight-team tournament brought players like Magic Johnson, Gary Payton and John Stockton to Portland.