LAS VEGAS -- Lonzo Ball had a turnover and two fouls before his first postseason game was 3 minutes old.
Nothing came easy for the star guard Thursday night, but No. 3 UCLA did just enough to advance in the Pac-12 Tournament.
Isaac Hamilton scored 22 points, and the Bruins held off rival Southern California 76-74 in the quarterfinals.
"It was tough," Ball said of his early foul trouble. "But credit to the coaching staff and teammates. You can't win this game with one person. They stepped up, Ham carried us on offense, and we got the stops we needed to win."
The Trojans, who never led and trailed by 14 in the first half, missed a tying 3-pointer and then two more shots in the final minute while trailing by three.
UCLA was held to 15 points below its nation-best scoring average.
"We haven't had too many tough shooting nights, but tonight was one of those," UCLA coach Steve Alford said of his team's 41-percent performance from the field. "We were able to get enough stops and hold them to (39) percent shooting."
Ball, the Pac-12 freshman of the year, finished with 12 points and seven assists. T.J. Leaf scored 14 points in his return after missing a game with a left ankle injury, and Thomas Welsh added 11 points and 11 rebounds before fouling out.
UCLA (29-3) earned its 10th straight win and secured a matchup with No. 7 Arizona in the semifinals on Friday night.
"We have an awful lot of respect for them," Alford said. "We know we're going to have to be better tomorrow night than what we were tonight."
Bennie Boatwright scored 11 points, but was 3 of 11 from the field and missed a tying 3 attempt with 34 seconds left.
"We missed a few layups and we missed a follow-up," USC coach Andy Enfield said. "Honestly, if one of those goes in and we get a few calls, maybe we have a chance to win."
Meeting in the tournament for the second straight year, the Los Angeles rivals played a much closer game than the last encounter, a 102-70 UCLA rout on Feb. 18. After USC started 1 of 14 from the field, it slowly got back in it thanks to UCLA's 10 first-half turnovers.
Enfield was confident going into the game that the Trojans had done enough to warrant an NCAA invite. That didn't change after the game. "You saw how we played tonight, you tell me," Enfield said. "I think we're a pretty good team."
It wasn't easy, but UCLA cleared the first hurdle in a tough three-step task. The Bruins are hoping to beat Arizona on Friday and potentially No. 5 Oregon in the final, a feat that could give them a No. 1 seed in the NCAA Tournament.
Alford spent much of the game pointing out the free-throw discrepancy to the referees. The Bruins didn't attempt their third free throw until 11:08 remained. The Trojans, who took it to the basket more, had 18 by then. USC finished with a 25-13 edge.
FOUL MOOD, TOO
USC's second-half angst was directed at the scorer's table after Enfield removed Stewart when it was announced he had four fouls. He had three, and Stewart quickly jumped off the bench and returned.
USC: The Trojans would like to return to the NCAA Tournament and make up for a dismal loss in 2016, when they blew a big lead and lost in the first round to Providence.
UCLA: Friday night will settle the season series with Arizona. Each team won on the other's home floor in the regular season.