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.
Devin Williams' decision last month to sign with an agent and enter the NBA draft has left West Virginia in a tough spot.
Florida State's student government has passed a resolution discouraging Seminoles fans from wearing Native American headdresses at games.
The second annual Gavitt Tipoff Games, eight games between members of the Big East and Big Ten to be played Nov. 14-18, will feature Villanova at Purdue in the opener.