No. 10 UCLA improves to 3-0 on the season with a 24-23 victory over No. 19 BYU. (1:17)

PASADENA, Calif. -- With quarterback Josh Rosen finally looking like a freshman, running back Paul Perkins was there to put No. 10 UCLA on his back.

And when Perkins finally got tired late in the fourth quarter, Nate Starks was there to carry the Bruins into the end zone.

Starks ran for a 3-yard touchdown with 3:25 remaining, Perkins rushed for 219 yards and a score, and UCLA rallied to beat No. 19 BYU 24-23 on Saturday night.

Rosen threw three interceptions in a shaky first half, prompting coach Jim Mora and offensive coordinator Noel Mazzone to lean on Perkins, the Pac-12's leading rusher last season. The often-overlooked redshirt junior responded with career highs in rushing yards and attempts, finishing with 26 carries.

"Paul's had some pretty darn good games, but what I thought was impressive about Paul was the toughness that he ran with," Mora said. "He carried people on his back, he moved the pile forward, he carried the ball a lot."

Perkins was set to receive his 27th carry of the night on the final drive for the Bruins (3-0), but Starks and the UCLA offensive line had the BYU defense in trouble. Starks had already ripped off runs of 31 and 22 yards on consecutive plays, and he scored the winning touchdown two plays later. The final six plays on the drive were all rushes by Perkins and Starks.

"The difference in the game was Perkins," said Cougars coach Bronco Mendenhall, who dropped to 1-6 against top-10 teams. "I thought he was really difficult to tackle and I thought he was a catalyst for their team. ... I think their running back was just very patient at creating holes and making us miss."

Tanner Mangum drove the Cougars (2-1) to the Bruins 42-yard line, but his fourth-down pass was intercepted by Myles Jack, allowing the Rose Bowl crowd of 67,612 to finally celebrate.

Mangum threw late touchdown passes to rally BYU to victory each of the previous two weeks.

Starks finished with 81 yards, and UCLA rushed for 296 to overcome Rosen's struggles. Rosen had two turnovers in the red zone, as linebacker Harvey Langi had a pick at the 5-yard line to end a promising drive, and safety Kai Nacua came up with an interception in the end zone in the final minute of the second quarter.

After going 5 of 15 for 52 yards in the first half, Rosen completed six of his final eight attempts for 54 yards after halftime, with a 19-yard touchdown to Jordan Payton early in the fourth quarter.

"Coming back to throw that slant-and-go to Jordan and put it right on the money . he didn't play well numbers-wise, but when it mattered he showed exactly who he is and that's exciting," Mora said.

It was a performance UCLA coaches expected would happen at some point this season and were glad it did before next week's Pac-12 opener at Arizona.

"You guys didn't really want to think it was coming, but it was coming," Mazzone said. "We can practice situations until we are blue in the face, but quarterbacks, kids don't grow up until they can go through the experience. It was a great learning experience for him."

Mangum had already been through those travails, throwing game-winning passes at Nebraska and against Boise State, and mostly outplayed his 18-year-old counterpart in the highly anticipated meeting of freshman quarterbacks.

Mangum was 30 of 47 for 244 yards, one touchdown and one interception, and added a reception for 4 yards when he caught his own batted pass in the fourth quarter. Though he was sacked four times, Mangum made several outstanding throws, including his 14-yard touchdown to Mitch Mathews in the third quarter after UCLA tied the game at 10.

Adam Hine rushed for 149 yards and capped BYU's opening drive with a walk-in 7-yard touchdown run. UCLA linebacker Kenny Young was ejected for targeting after leading with his helmet on a sliding Mangum during the possession, and initially refused to leave the field before sprinting to the locker room.

Michael Davis recovered a surprise onside kick, and though that extra possession did not result in points, it set the tone for an aggressive first half by BYU. Langi played on both sides of the ball and finished with eight tackles and two interceptions, and carried the ball twice for 8 yards.

Late in the game, however, Mendenhall sent Trevor Samson out to kick a 32-yard field goal on fourth-and-3 from the Bruins 14-yard line. Samson hit his third field goal of the night for a 23-17 lead, leaving Perkins and Starks a chance to carry UCLA to the win.