The Gaels conclude the first half of conference play 14-6, 6-2 West Coast Conference, while BYU improves to 14-6, 5-2 WCC.
"BYU is a long, physical team that gave us fits in our post-up game," said head coach Paul Thomas. "We did not get enough stops in the second half to win the game."
Saint Mary's controlled the boards and the paint for much of the first half, but a cold stretch to start the second half ultimately let the Cougars escape with the victory.
Jackie Nared led the Gaels with her 10th double-double of the year with 18 points and 11 rebounds. Kate Gaze and Danielle Mauldin added 10 points apiece. Andrea Bailey played well off the bench with a season-high eight rebounds in just 10 minutes of action.
BYU was led by Kim Beeston with 14 points while Haley Steed added 14 points and nine assists.
Saint Mary's led by seven points in the first half with 5;46 remaining. Amanda Arter hit a three ball on the Gaels' final possession to push the SMC lead up to six points but Steed came back to answer with a three ball just before the half time buzzer as the Gaels led 35-32 at the break.
The Cougars scored the first nine points of the second half and the Gaels could not muster a field goal for nearly the first six minutes. BYU built a nine point lead with 10:00 remaining and the Gaels would pull within five points on several occasions but could not pull even.
SMC outrebounded BYU 48-36 and outscored BYU 22-12 in the paint.
Saint Mary's is back in action on Thursday when it hosts Portland at 6:00 p.m. in McKeon Pavilion. After the Gaels face the Pilots, SMC will host the same BYU team on Saturday night, Feb. 9th.