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Scott G Winterton, Deseret News
BYU's Bronson Kaufusi and Ian Harward look on as the final seconds tick away as BYU falls to San Francisco 99-87 Saturday, Feb. 9, 2013 in the Marriott Center.

PROVO — They say bad things come in threes, and that certainly was the case for BYU Saturday night at the Marriott Center.

The Cougars squandered a 15-point lead in the second half and collapsed under the weight of San Francisco's spectacular 3-point shooting barrage.

In the end, the Dons knocked off BYU, 99-87, before a stunned crowd of 15,477.

Just when it looked like the Cougars' season couldn't get any worse, it did. Coming off a painful loss at San Diego last Thursday, BYU started well but failed to finish.

San Francisco, which hadn't played in a week, seized control in the final 20 minutes. The Dons scored 60 second-half points, shot 72 percent from the floor in the second half, and nailed 9 of 10 shots from 3-point territory in the second half.

And after trailing by 15 early in the second half, USF led by as many as 16 in the closing seconds — an amazing 31-point turnaround.

Overall, USF hit 14 3-pointers, including 12 of its final 13 attempts from long distance.

"You definitely have to give them a lot of credit. We haven't seen a team come in and shoot like that, especially in a half," said forward Brandon Davies. "It's definitely hard to swallow. They were shooting lights out. We had a couple of letdowns defensively, but they were making shots. The littlest letdown can turn into disaster."

BYU fell to 18-8 overall and 8-5 in the West Coast Conference. San Francisco improved to 11-13 and 4-7.

USF guard Cody Doolin, who scored 16 points and had eight assists, called it the "best win I've ever been a part of."

The Dons' De'End Parker came off the bench to score a game-high 23 points, including three 3-pointers, while Chris Adams and Avry Holmes each chipped in 17. Adams drilled 5 of 6 3-pointers and Holmes was 3 of 5.

The Cougars were cruising early in the second half, with a 54-39 lead, and they appeared to be running away with the game.

But seconds later, Adams buried a 3-pointer to kick-start USF's big second-half run. By the time Parker nailed another 3 with a little less than six minutes remaining, the Dons had taken their first lead since early in the game, 72-70.

"San Francisco played a great second half," said BYU coach Dave Rose. "We had a difficult time containing the ball in whatever defense we were in. They drove us pretty good and kicked it to open shooters. They really got on a roll there in the second half. We had a hard time matching it and lost the momentum. They didn't let up. Whatever we did defensively, they had an answer for."

Doolin, the Dons' crafty point guard, made things happen by penetrating and kicking the ball to open shooters.

"We let him get all over the floor," Davies said. "Every single one of us had a chance to guard him, and we let him do what he wanted to do. That's what great players do. He's tough to get stopped. He's their spark plug."

USF hit 3-pointers in a variety of ways against BYU's defense.

"Some of them were hands-in-their-faces and they just made great plays," said Cougar guard Brock Zylstra, who scored a team-high 18 points. "Others, we were slow on rotation. That was a great shooting exhibition by them and they took us out of our game."

The first half featured plenty of physical play by both teams. At one point, BYU guard Tyler Haws was whistled for a technical foul after he reacted to USF's rough defense against him. But the Cougars led at halftime, 48-39.

In the second half, BYU opened with six straight points to go up by 15. But it was all San Francisco from there, as the Cougars shot just 35.5 percent in the second half.

"That's just them. They don't give up," Zylstra said of the Dons. "That's coach (Rex) Walter's mentality and his guys follow how he is. He's a fighter. His guys are fighters. … The flow wasn't the way it was in the first half on offense for us. Their physicality was a big part of that. Our (shooting) percentage went down because the flow wasn't BYU's flow."

"It seemed like they were a step quicker in the second half," Rose said. "We had the momentum in the second half and we let it slip away. We didn't consistently keep scoring and they got on a roll. It shifted quick."

BYU hosts Portland next Saturday (7 p.m. MST, BYUtv).