Holt was 5 of 9 from 3-point range for the Gaels (14-4, 3-1 West Coast). Dellavedova scored 18 points. James Walker III had 13 points and seven rebounds, and Mitchell Young had 10 points and seven rebounds. Brad Waldow had seven rebounds.
BYU (14-5, 4-1) led 34-27 at halftime. In the second half, the Gaels were 7 of 11 from 3-point range.
Dellavedova made a free throw, tying the game at 65 with 1:48 to play. Tyler Haws put BYU up with a jumper, but Dellavedova scored, tying the game again. Haws hit a jumper with 2 seconds to play. Dellavedova hit a 3-pointer at the buzzer to give Saint Mary's the win.
The play made the top position on ESPN SportsCenter's popular "Play of the Day" feature.
Haws had 23 points, seven rebounds. Matt Carlino had 16 points. Brandon Davies added 12.