"They believe they are going to win at home, and they make the plays," Rose said.
The Cougars dropped to 20-9 overall, 9-5 in West Coast Conference play, but remained in third place in the league. The loss means BYU will not finish among the top two in the league and will not get a bye into the tournament semifinals. The Gaels (23-5, 12-2) will, along with No. 3 Gonzaga.
Matthew Dellavedova led Saint Mary's with 20 points and Beau Levesque added 17, while Brandon Davies had 25 for BYU, going 10 for 16 from the field. He also grabbed nine rebounds.
But it wasn't enough, as the Cougars missed two free throws, committed a questionable offensive foul away from the ball and badly missed a jumper with the game on the line.
"They just made the plays down the stretch to win," said BYU's Tyler Haws, who scored 12 points, the only other Cougar in double figures. "We gave ourselves chances to win, but they made the plays."
Davies' basket with 2:09 remaining got the Cougars to within two points, 59-57, but Matt Carlino missed a pair of free throws with 1:20 left and the Gaels made enough free throws in the final minute to keep the Cougars at bay.
Saint Mary's enjoyed a sizeable advantage at the free-throw line, going 22 of 26 from there. The Cougars made three more field goals, 21-18, but were just 12 of 19 from the line as Saint Mary's got into the bonus and even the double-bonus early in both halves. BYU even outshot the home team, 51.2 percent to 36.0, but lost the rebounding battle 33-26 and made just three 3-pointers to six from Saint Mary's.
"Both teams were playing really physical," Rose said, when asked about the free-throw disparity. "....But you gotta fight through it and there are some things you can control and some things you can't. ... But yeah, they did get to the line a lot."
The Cougars took a 44-43 lead with 11:09 remaining on Brock Zylstra's free throw, but a pair of free throws from Levesque put the Gaels in front again 17 seconds later. The Gaels led by six a couple of times, but Zylstra's 3-pointer with around five minutes remaining got the Cougars to within one, 54-53.
Chances to take the lead fizzled the next two possessions as Davies' shots were blocked near the rim. The Cougars wanted a whistle on both, but didn't get them.
"That's on me," Davies said. "The way the game was officiated, I got to go harder to the rim."
Davies scored 12 points on 6-of-9 shooting in the first half to give the Cougars a 32-28 lead at the break.
The Cougars shot 13 of 22 in the first half and held the Gaels to 9-for-26 shooting, which is why they had the lead at halftime. That, and they led the rebounding battle, 15-14.
Dellavedova, who hit the buzzer-beater to beat BYU in Provo, was 3 for 8 from the field for eight points in the first half and finished just 6 of 14. But he drew the offensive foul on Haws with around a minute left when the Cougars trailed 60-57.
Haws called the call "ridiculous."
But it stood, and the Gaels prevailed for the fourth straight time over the Cougars.
Storylines Saint Mary's 64,BYU 57
R IN SHORT • Saint Mary's makes more plays down the stretch than BYU and takes a hard-fought 64-57 win over the Cougars.
KEY MOMENT • Matt Carlino misses a pair of free throws with 80 seconds remaining that would have tied the game.
KEY STAT • Saint Mary's goes 22 for 26 from the free-throw line.