LOS ANGELES -- A technical foul against senior co-captain Lodrick Stewart undid everything Southern California had built for 75 minutes against No. 2 UCLA.
Stewart's angry spike sent the ball sky-high with 4 1/2 minutes left and with it went USC's hopes of upsetting its crosstown rival.
Darren Collison tied his career high with 17 points and the Bruins capitalized on Stewart's impulsiveness by scoring five straight points to win 70-65 Wednesday night.
With a victory, the Trojans (18-7, 8-4) could have tied UCLA (21-2, 10-2) for the Pac-10 lead, but instead they dropped to third behind idle Washington State (8-3).
"We're encouraged we can play the second-ranked team in the nation for 75 minutes, but not 80," said USC coach Tim Floyd, who refused to discuss the officiating.
UCLA extended its Pauley Pavilion winning streak to 18 games as the Pac-10's only undefeated team at home.
Arron Afflalo scored 13 of his 16 points in the second half, including two free throws that gave UCLA the lead for good with 4 1/2 minutes left. His jumper with 4 seconds left rallied the Bruins to a 65-64 win last month at USC.
"I was never worried because we're a group that's used to winning," Afflalo said. "That's what we expect of ourselves. They kept making plays, so we have to credit ourselves for staying around. We did a good job of fighting and staying strong."
Luc Richard Mbah a Moute added 11 points and 10 rebounds for the Bruins.
Nick Young led USC with 20 points, Gabe Pruitt added 16 and Stewart 13.
Stewart was whistled for spiking the ball with 4 1/2 minutes left in front of a raucous, season-high crowd of 12,810 that included former UCLA coach John Wooden and Gov. Arnold Schwarzenegger.
"I don't even want to talk about that," Stewart said. "A couple shots here and there, easy layups we missed, a couple plays we could have had back that would have made the difference in us winning the game. They played us great and we played them great."
It was a tough ending for what has already been a bad week for Stewart. He found out on Monday that his great-grandfather had died and his mother was hospitalized in Mississippi because of a nervous breakdown.
Floyd would only say that he was disappointed about Stewart's technical. But Young supported his teammate.
"I thought coach Floyd got it at first," Young said. "It was a tough call. We all felt down for him. That's one of our leaders on the team."
USC led by seven points early in the second half before things got tight.
Trailing by two, Josh Shipp scored and got fouled by Young, who picked up his fourth with 4:25 left. Before Shipp could step to the line, though, Stewart earned the technical. Afflalo made both of those for a 54-52 lead, then Shipp completed his three-point play.
"That was big for us," Collison said. "We knew we didn't play our best game. We're just fortunate we came out with the victory."
Collison drove the lane for a one-handed layup that kept UCLA ahead 59-54. USC's RouSean Cromwell committed an intentional foul as the Trojans' frustration grew.
Dwight Lewis and Pruitt hit 3-pointers in the closing seconds, but UCLA proved steady at the foul line, going 10-for-10 down the stretch to preserve the win.
"It's pretty frustrating," Pruitt said. "They made a couple plays at the end. It always happens like that. We just got to get past that hump. Hopefully, we'll see them in the postseason (Pac-10) tournament."
The Bruins got within one for the first time with an 8-2 run, including four in a row by Mbah a Moute, whose fastbreak layup came off his own steal.
The teams traded baskets before Afflalo hit a 3-pointer from deep in the left corner -- just his second field goal of the game -- that tied it at 46 and ignited the crowd.
Defense led to UCLA's first lead of the game. Alfred Aboya took the ball away from Pruitt and heaved a long pass to a streaking Afflalo, who dunked with abandon for a 50-48 lead with 5:51 remaining.
But Pruitt got fouled by Collison, who crouched in frustration, and made both for another tie at 50.
The Trojans came out aggressively to start the game, pulling away to a 20-10 lead while shooting 82 percent from the floor. They scored 11 points off UCLA's nine turnovers in the half.
The Bruins struggled offensively, missing several open shots until they outscored USC 11-4 to end the half trailing 30-29.
The Trojans failed to get a shot off on their final possession before the shot clock expired. Attempting to give UCLA its first lead heading into the lockerroom, Collison's midcourt shot hit the rim and bounced away.