Eric Musselman marched into the visiting locker room at Pauley Pavilion, smoldering with each step, and went straight to the whiteboard. He grabbed a marker and wrote the score of Saturday night’s rivalry loss to UCLA, one of USC’s worst of the season. He let it sink in: 90-63.

The score on its own cut deeper than any words the coach could use in that moment. Though, he had plenty with four letters rattling around in his mind.

“Just another night of somebody scoring 90 points,” he said later, shaking his head.

At the end of a roller coaster regular season, the Trojans tripped over the finish line Saturday, and in the aftermath, Musselman had little more than exasperation to offer up in response. The loss to UCLA left USC sitting below .500 for the first time in Musselman’s debut season. It’s just the second time in a decade that USC or its coach have finished with fewer wins than losses in a season.

The result won’t matter much for USC’s standing in next week’s conference tournament. That invite was already clinched Thursday, with USC bound for one of the bottom two spots. The Trojans will face either Ohio State, Rutgers or Minnesota, depending on how Sunday’s games play out.

But to Musselman, the way in which USC lost Saturday was especially discouraging. It was one of the largest margins of defeat in a storied rivalry that stretches back nearly a century. If not for a 9-0 run to finish the game, it might’ve climbed even closer to infamy.

That was unacceptable to Musselman, who called out his players for not respecting the rivalry with UCLA.

“I felt like the rivalry, they didn’t understand, even in Game 1. And they certainly didn’t understand today,” Musselman said. “We played the game like we were playing any normal game, and it’s not a normal game.”

By the final buzzer, the coach’s voice had gone hoarse, largely from screaming at his defense, which completely unraveled once again.

UCLA knocked down 62% of its shots from the field on Saturday, tied for its best percentage of the season. For USC, it was by far the worst it has defended from the field — a full 5% higher than in any other game season.

The porous defense from USC started early, as the Trojans fell into a 14-2 hole, and only worsened in the second half, as they allowed the Bruins to unleash a 51-23 blitzkrieg that buried them for good.

That was nothing new, Musselman said. USC has allowed its opponents to shoot at least 48% from the field in five of its last six games.

UCLA’s Sebastian Mack, center, drives between USC’s Jalen Shelley, left, and Desmond Claude during the second half Saturday.

(Allen J. Schaben / Los Angeles Times)

Musselman wondered if UCLA might’ve shot the same percentage with no one guarding them at all.

“It’s been bad all year,” Musselman said. “Just look at the numbers. People are having career nights.”

Indeed, five Bruins would score in double figures, while Eric Dailey Jr. led all with 25. A 21-point showing in the loss from USC’s Wesley Yates III could only do so much to stem the tide.

Yates was the only Trojan eliciting any praise Saturday, as UCLA coach Mick Cronin singled him out as USC’s “best player, period.”

It didn’t help its hopes of hanging with UCLA that USC also turned the ball over 20 times, in addition to its dismal defense. It was the most turnovers USC has committed in a game under Musselman.

USC coach Eric Musselman reacts during Saturday’s loss to UCLA at Pauley Pavilion.

(Allen J. Schaben / Los Angeles Times)

This wasn’t exactly ending on a high note. And its coach wasn’t going to sugarcoat that fact Saturday night.

Hope isn’t exactly running high ahead of next week’s Big Ten tournament. Even Musselman was wondering aloud about what his team needs for next season.

“We’ve got to get a lot better,” he said. “I know that. I’m positive about that. And we will. We’ve got to take better care of the basketball. We’ve got to get some defenders in here. We’ve got to build a team of competitors.

“It’ll be a busy time for us here in two weeks.”