Las Vegas • Having held off San Diego in overtime a month ago in rainy San Diego and a week ago in wintry Provo, third-seeded BYU didn’t really want to see the West Coast Conference’s No. 7 seed again, even if the Toreros were playing in their third game in as many nights.

But that’s the hand the Cougars were dealt a few blocks away from the famed Las Vegas Strip in a West Coast Conference tournament quarterfinal, and the result was altogether different from the regular-season meetings.

Like, night and day different.

San Diego took out its frustrations for three straight losses to the Cougars, including one in last year’s quarterfinal, and then some with a 80-57 beatdown at Orleans Arena on Saturday night.

“This wasn’t a [true] seventh-seeded team,” BYU coach Dave Rose said of the red-hot Toreros. “They played the top four teams in our league twice, with the unbalanced schedule. Our entire staff thought that.”

San Diego led by as many as 44 points in the second half, but the Cougars rallied in garbage time to avoid the largest margin of defeat in Rose’s 14-year tenure. The Cougars lost 102-68 at No. 1 Gonzaga on Feb. 23, which remains Rose’s worst loss.

“Not at all,” Rose said when he was asked if he had an inkling the Cougars would play their worst game of the season. “We practiced well, we prepared well.”

Then they played horribly. Rose was quick to credit San Diego for being a “really determined, together group,” and playing “terrific basketball," but said the Cougars dropped their heads early after a horrible start and reverted to old habits that plagued them in December.

“When you don’t score, that’s a part of the game that’s pretty important,” he said.

The Toreros (21-13) advance to Monday’s semifinals against No. 2 seed Saint Mary’s, while BYU (19-13) limps back to Provo and awaits an NIT bid that might not come if anybody from that selection committee bothered to stay up late to watch this debacle.

Asked if BYU would accept a bid to a lesser tournament such as the CBI or CIT, Rose was noncommital, noting that the Cougars have never been in that position before in his tenure.

“We will see,” he said.

The Cougars were never in the game. Not even close. They missed their first six shots, then turned the ball over on their seventh and eighth possessions. Looking nothing like a team that could have easily used fatigue as an excuse, San Diego made five of its first six shots and jumped to a 13-0 lead before BYU finally scored with 14:24 left in the first half on a Yoeli Childs jumper.

“A week ago, we sat in a locker room up in Provo after they beat us pretty good,” said USD coach Sam Scholl. “... We hit the reset button on Monday.”

TJ Haws missed his first six shots and didn’t score until he made two free throws with 4:16 left in the first half. By then the Toreros had a 36-15 lead. Rose said Thursday that Haws was showing no ill-effects from a collision late in the win over San Diego last Saturday, but the junior was clearly not himself.

Haws finished with 10 points on 2-of-12 shooting, after scoring 61 points in the previous two games against USD.

San Diego took a 46-19 halftime lead on Finn Sullivan’s last-second layup. The Toreros shot 53 percent in the first half and held BYU to 25 percent. It was the Cougars’ lowest-scoring half of the season and fifth-largest halftime deficit ever.

Isaiah Pineiro had 15 points and seven rebounds in the first half alone, and former Ute Isaiah Wright added 11 in the first 20 minutes. Pineiro finished with 27 points and Wright had 15.

“Isaiah Wright did a tremendous job on TJ,” Pineiro said.

USD dropped Santa Clara 62-45 late Friday night to advance. The Toreros beat Portland 67-47 in the first round Thursday. Little did anyone know they would have an easier time with BYU, which beat them 88-82 in San Diego and 87-73 in Provo.

Scholl praised the tournament format, calling it “outstanding,” but noted: “Of course, I am saying that after winning three games.”

From the same seat a few minutes later, Rose ripped on the format, questioning why a team would have only 20 minutes to shoot at a gym, as BYU did, despite coming in with a No. 3 seed. The team that played the night, or nights, before has won all four games; Pepperdine upset No. 4 seed San Francisco in Saturday’s early quarterfinal.

“Somebody has to re-evaluate this,” Rose said. “There’s too much on the line.”

Childs finished with 14 points in what may have been the junior’s final WCC tournament game. Childs was hit with a technical foul for protesting a non-call and went to the bench with 12:50 remaining, never to return. He had 14 points and six rebounds.

The Cougars dropped to 9-8 in WCC tournament games and are in danger of not getting to 20 wins for the first time in Rose’s 14 seasons.