BOULDER, Colo. (AP) — Sam Darnold has seen plenty of what cornerback Ajene Harris can do in practice. He's just thankful he doesn't have to face him when it counts.

Darnold tossed two touchdown passes and ran for another, Harris intercepted two passes, including one he returned for a score, and No. 15 Southern California beat Colorado 38-24 on Saturday to wrap up the Pac-12 South title.

"Always good to have someone like him on defense," Darnold said.

The same can be said of Darnold — on offense, of course — after he threw for 329 yards and improved to 18-3 as a starter.

"I've really enjoyed his leadership, whether it's good times or bad," USC coach Clay Helton said. "When you're the quarterback at USC and to have that much pressure on you and do it with so much class and character on a weekly basis, whether things are going good or bad, and perform for his brothers? He's the definition of believing in the team's success over individual success."

USC (9-2, 7-1 Pac-12, CFP No. 11) led 27-0 in the third quarter, but needed to weather a late Colorado comeback. The Trojans blocked two field goals to move to 12-0 against the Buffaloes (5-6, 2-6).

Juwann Winfree had a big day for Colorado by hauling in TD passes of 79 and 57 yards. Steven Montez was tackled on a fourth down play near the USC goal line on Colorado's final possession with just over a minute remaining. Montez said he thought it was first down. The confusion stemmed from the fact Montez thought the Buffs picked up the first down.

"It was fourth down — all the way," Colorado coach Mike MacIntyre said. "I don't know."

A pivotal play in the game was when Colorado tried to get something going with about a minute left before halftime and down 14-0. Montez forced a pass to the outside that Harris stepped in front of, tip-toed along the out-of-bounds line and headed into the end zone.

Harris had another interception in the fourth quarter that nearly went for a score. As he was being tackled, Harris pitched the ball to Marvell Tell III, who took it about 27 yards for a TD. The replay booth took a look and ruled that Harris' knee was down before the pitch.

"It would've been real sweet for the whole squad," Harris said. "What a great win for us."

USC will play in the conference title game on Dec. 1 in Santa Clara, California. The representative from the north remains up in the air.

"There's still a lot out there that we have to get ready for," Helton said. "We're going to celebrate tonight and go back to work tomorrow."

THE TAKEAWAY

USC: This should please coach Clay Helton — the Trojans turned in big plays on offense, defense and special teams.

POLL IMPLICATIONS

USC will be trending up after turning in a dominant first half and something less than that in the second.

THIS & THAT

The temperature at kickoff was 59 degrees. The last time the Trojans played a game in the snow was Nov. 30, 1957, at Notre Dame. … The last time USC blocked two field goals in a game was Nov. 4, 2011, against Colorado.

UP NEXT

USC: Closes out the regular season against UCLA.