Soma Vainuku, Leon McQuay III, Charles Burks

Soma Vainuku (31) enjoys the moment with USC teammates Leon McQuay III, left, and Charles Burks during the first quarter Saturday in Boulder. (Doug Pensinger / Getty Images / November 23, 2013)

BOULDER, Colo. -- USC fullback Soma Vainuku continued his knack for making big plays Saturday night during the Trojans' 47-29 victory over Colorado.

The third-year sophomore from Eureka, who has excelled on special teams this season, blocked a first-quarter punt into the end zone for a safety that gave the Trojans a 9-0 lead.

Then late in the game, Vainuku broke loose on a 52-yard run for the game's final touchdown with 2:19 to play.

Vainuku also blocked punts against California and Arizona; the one at Cal was returned for a touchdown by cornerback Josh Shaw.

He finished Saturday's game with 70 yards in five carries, and also caught two passes for 11 yards.

Bailey, Williams make key plays

USC safety Dion Bailey intercepted a pass and defensive end Leonard Williams forced a fumble to set up second-quarter touchdowns that helped the Trojans take a 23-0 halftime lead against Colorado on Saturday night at Folsom Field.

Williams, who has been nursing a shoulder injury, sacked Colorado quarterback Sefo Liufau with 7:22 left in the first half and end George Uko recovered the ball for the Trojans. Tailback Javorius Allen scored five plays later to put the Trojans ahead, 16-0.

Bailey, who had a key interception last week against Stanford, picked off a Liufau pass with 2:34 left in the second quarter. The play set up Cody Kessler's 20-yard touchdown pass to Nelson Agholor for a 23-0 lead.

Bailey has a team-best five interceptions.

Tight ends shine

Tight ends Xaxier Grimble and Randall Telfer played leading roles in the No. 23 Trojans' victory.

Grimble, a junior from Las Vegas, had a season-high six catches, all in the first half, for 46 yards, including four during a second-quarter drive that ended with Cody Kessler's touchdown pass to Nelson Agholor. Grimble's previous high in a game this season was three catches.

Telfer, a junior from Rancho Cucamonga, caught a 10-yard scoring pass early in the third quarter to give USC a 30-7 lead.

Lee stays behind

Receiver Marqise Lee, who suffered a shin injury during last week's victory over Stanford, did not travel with the Trojans for Saturday night's game.

Lee, the 2012 Biletnikoff Award winner, stayed in Los Angeles to continue rehabilitation, USC announced. He is expected to ready for next Saturday's game against UCLA at the Coliseum.

Lee has experienced numerous injuries this season. He hurt a shoulder during training camp and suffered a knee injury against Arizona State on Sept. 28. He aggravated the knee injury Oct. 19 against Notre Dame.

Lee said he suffered the shin injury late in the fourth quarter of the Trojans' 20-17 upset of Stanford. But he came back to catch the key fourth-and-two pass that kept alive the Trojans' game-winning drive.

Lee, who set a Pac-12 record with 118 catches last year, has 44 receptions and has scored two touchdowns.