Aaron Bright's pair of free throws with 23.9 seconds left extended Saint Mary's (15-3, 7-0 West Coast) lead to five, and BYU missed a pair of 3-point attempts in the final seconds. The Gaels will visit No. 3 Gonzaga on Thursday with both teams undefeated in conference play.
Garrett Jackson added 20 points and nine rebounds for the Gaels. Saint Mary's led the entire the second half, but BYU (15-6, 5-3) rallied within 75-72 with 2:25 left.
Skylar Halford hit a transition 3-pointer off Corbin Kaufusi's block to get the Cougars back within three at 80-77.
Waldow moved ahead of Robert Haugen (1985-89) into sixth place on Saint Mary's career scoring list with 1,523.