Davies scored a game-high 25 points, but it wasn't enough to knock off the Gaels, who were led by guard Matthew Dellavedova's 20 points.
BYU was coming off a dramatic, last-second victory over Utah State at home Tuesday, and the Cougars carried over that momentum with a strong first-half effort against the Gaels to lead by four points at the intermission.
But the foul-prone Cougars couldn't overcome Saint Mary's in the second half.
Dellavedova, who drained the game-winning shot at the buzzer last month in Provo, struck again Thursday. He knocked down a big 3-pointer from the corner with 6:40 left in the game that propelled the Gaels to a 52-46 lead. Later, with 2:20 remaining, he hit a floater in the lane that put Saint Mary's up by four, 59-55.
BYU trailed 59-57 with 1:20 left when guard Matt Carlino missed a pair of free throws. Dellavedova made 1 of 2 two free throws to make it 60-57. The Cougars' next two possessions ended with a turnover and a missed shot by Tyler Haws.
Saint Mary's improves to 23-5 overall and 12-2 in the West Coast Conference. BYU drops to 20-9 and 9-5.
The Gaels swept the season series over the Cougars for the second year in a row. BYU is now 0-4 against the Gaels since joining the WCC.
The last time the Cougars defeated the Gaels was a 74-73 victory in the South Padre Invitational in November 2010.
With the win, Saint Mary's clinched at least the No. 2 seed in the upcoming WCC tournament in Las Vegas.
Things got chippy early on. The game was less than one minute old when Brock Zylstra administered a hard foul on St. Mary's Mitchell Young under the basket, preventing a layup. Young reacted by bumping into Zylstra, drawing a technical foul.
After Haws hit both technical free throws, Craig Cusick buried a 3-pointer to put the Cougars ahead, 7-3. Later, after Davies scored back-to-back buckets, BYU led 13-6.
The Gaels responded by scoring seven straight points to tie the game at 13-apiece. Carlino's alley-oop pass to Davies for a dunk lifted the Cougars to a 19-18 advantage midway through the half.
During one stretch, Saint Mary's went seven minutes without a field goal. But BYU suffered its own scoring droughts as well.
The two teams traded leads before BYU reserve Raul Delgado drilled a 3-pointer with a little more than three minutes left in the first half to put BYU up, 28-25. Nate Austin and Davies scored the final two buckets of the half, and the Cougars led at intermission, 32-28. At halftime, Davies had a game-high 12 points.
Davies picked up where he left off to start the second half, scoring a basket that saw the Cougars take a six-point lead, their biggest of the game, 34-28.
But the Gaels went on a 7-0 run to re-take the lead. Saint Mary's took the lead for good midway through the half.
Zylstra cut the deficit to one, 54-53, when he connected on a 3-pointer with five minutes remaining. The Gaels' Beau Levesque answered with a 3-pointer to give Saint Mary's a 57-53 edge.
BYU's next game is next Thursday, when the Cougars host No. 3 Gonzaga.