No. 21 Colorado (4-1, 2-0 Pac-12) at USC (2-3, 1-2), 4 p.m. (Pac-12 Network)

Line: USC by 4½.

Series Record: USC leads 10-0.

WHAT'S AT STAKE

Colorado's first game as a ranked team since Nov. 6, 2005, is an opportunity to prove its resurgence is for real. The Buffaloes have never won three Pac-12 games in a season and have never beaten USC, one of the nation's most glamorous programs. The Trojans are hoping to bounce back from their 1-3 start to the season with back-to-back victories over ranked teams.

KEY MATCHUP

Colorado RB Phillip Lindsay vs. USC LB Cameron Smith. Lindsay is the busiest ball-carrier in the Buffs' much-improve rushing offense, while Smith is the leading tackler on a defense that held Arizona State to 105 yards rushing last week, dominating the line of scrimmage.

PLAYERS TO WATCH

Colorado: DT Jordan Carrell. The JUCO transfer is quietly having a huge senior season on perhaps the Buffs' best defensive line in a decade, making 21 tackles with 2 1/2 sacks and a host of quarterback pressures.

USC: WR JuJu Smith-Schuster. The Trojans' top pass-catcher broke out with new quarterback Sam Darnold for 123 yards receiving and three touchdowns last week.

FACTS & FIGURES

Colorado is keeping quiet about whether hobbling QB Sefo Liufau or freshman backup Steven Montez will start. ... USC has outscored Colorado 360-128 in the schools' first 10 meetings. ... Last year in Boulder, the Trojans rallied in the second half for a 27-24 win after Liufau got hurt, but Colorado led for more than half of the game. ... Colorado is the only unbeaten team in conference play in the Pac-12 South. Buffs haven't led a conference division by themselves since Oct. 6, 2007, in the Big 12 North. ... Colorado hasn't started a season 5-1 since 2007. It has lost nine straight games in California since 2002. ... This was supposed to be one of the easier games on the schedule for the Trojans, whose schedule is among the nation's toughest this season. ... Darnold passed for 352 yards last week against Arizona State in the freshman's first home start.

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AP college football website: collegefootball.ap.org