Kyle Collinsworth leads BYU with 14 points and six rebounds. Tyler Haws is the only other Cougar in double figures with 11 points and four boards.
The Cougars struggled with turnovers early in the half, giving up four within the first two minutes of play. During that stretch Saint Mary's jumped out to an early 8-2 lead.
The Gaels took a double-digit lead with at 19-8 with 12:07 remaining in the half from a pair of Brad Waldow free throws.
Frank Bartley IV cut Saint Mary's lead back to single digits at 28-19 from a fast break layup.
An Anson Winder 3-pointer sparked BYU's offense and helped the Cougars come back within two from a 9-2 run.
Haws then hit a 3-pointer of his own to tie the game at 35 with under two minutes remaining and a Collinsworth bucket gave BYU its first lead of the game at 37-35.