Stumbo came off the bench to score 13 points and Conor Riordan added 16 for the Storm (1-1), who came back from a 10-point deficit to even their record on the young season.
Simpson led 87-86 when Stumbo nailed a deep 3 from the left wing with 45 seconds left. Kobe Wands missed on the next possession for Westminster, Stumbo secured the rebound then made a pair of free throws for the final margin.
Stu Hollandsworth scored a game-high 25 points to lead the Bluejays (0-1).
A layup by Romo Tabb gave Westminster a 55-45 lead with 17:00 left in the game. Rajewski responded with his fourth 3-pointer to spark a 10-0 Simpson run. He added a layup, Stumbo made a pair of free throws and Taylor Filbert converted an and-one on a tip-in to tie it 55-55 with 14:34 left.
Another Rajewski 3 put Simpson ahead 87-83 with 1:14 left, but Wands drew a foul on a 3-pointer and made all three from the charity stripe to pull Westminster within one.
Rajewski went 5-for-6 from beyond the arc and Filbert narrowly missed a double-double with nine points and a team-high eight rebounds for the Storm.
Simpson plays North Park in the first game of the North Park Tournament on Friday, Nov. 16 in Chicago, Ill. Start time is set for 3:30 p.m.