SANTA CLARA, Calif. (AP) — With the Pac-12 championship hanging in the balance, USC delivered a goal-line stand followed by a 99-yard drive that gave the Trojans their first conference title in nine years.

Sam Darnold's 54-yard pass to Michael Pittman Jr. keyed the long drive after Uchenna Nwosu preserved the lead with the defensive stop that led No. 10 USC to a 31-28 victory over No. 12 Stanford on Friday night.

"It was time to dig deep and win a championship," coach Clay Helton said. "When you're trying to win one, those are the plays that are going to define you and define your football team."

The Trojans (11-2, No. 10 CFP) led 24-21 when the Cardinal (9-4, No. 12) drove down the field in position to tie the game or take the lead.

But facing a third down from the 2, Stanford kept star back Bryce Love on the sideline with his gimpy ankle to rely on short-yardage back Cameron Scarlett instead. Scarlett ran on successive plays, gaining 1 yard on third down and then being stopped just short of the end zone on fourth.

"The bottom line is we had opportunities and we didn't make enough plays," coach David Shaw said. "We made enough plays to keep it close but not enough plays to win. The sequence of fourth-and-1 to take the lead in the Pac-12 championship game, there's no hesitation at all. That's what we're going to do."

Shaw figured at worst, Stanford would come out of that situation with a defensive stop and good field position on the ensuing drive but those hopes ended when Darnold delivered the offensive play of the game.

After Ronald Jones II gained 1 yard on first down, Darnold dropped back to pass and quickly was under pressure. He stepped up and appeared ready to run before launching a pass to Pittman to get USC out of trouble.

"That's kind of what you expect from Sam, to make those crazy plays," Pittman said. "That's why he's one of the best players in the country."

Jones finished that drive with an 8-yard run that made it 31-21 to cap a productive night where he ran for 140 yards and two touchdowns to give USC its first Pac-12 title since 2008.

Darnold was 17 for 24 for 325 yards with TD passes to Pittman and Tyler Vaughns to lead the way for USC.

The win gives USC a season sweep against Stanford and will likely send the Trojans to the Fiesta Bowl. USC still holds out hope for a spot in the four-team playoff if there are several upsets in other conference title games on Saturday but the chances appear to be remote.

"However we get ranked is not up to us, but we're just going to continue to compete, and that's all we can do," Darnold said.

THE TAKEAWAY

USC: The Trojans had a balanced offensive performance with Pittman catching seven passes for 146 yards and Jones doing solid work on the ground. The defense came up with the big stop at the goal line. 

CLINCHER

USC still needed one more play from Darnold to put the game away after Stanford's onside kick went out of bounds. On fourth-and-2 from the Cardinal 32, Helton called for a pass and Darnold hit Josh Falo for a 15-yard gain that allowed the Trojans to run out the clock.

"We were playing for a Pac-12 title, and there was no question in my mind that we were going to go for it and end the game right there," Helton said.

MAKE A CASE

USC might need Wisconsin and Oklahoma to lose Saturday in their title games to have a shot at the playoff. But the Trojans would have to jump over several teams to do that, including Ohio State if the Buckeyes win the Big Ten, and Alabama, which is in fifth place with one loss but didn't make the SEC title game.

"I think we will be in the conversation," athletic director Lynn Swann said. "We're the Pac-12 champions so whenever that conversation is I think we'll be in it. Whether we're going to be in the top four or not, that's not our decision. We'll live with whatever they decide."

UP NEXT

Both teams will get their bowl bids on Sunday with USC likely headed to the Fiesta Bowl and Stanford expected to go to the Holiday or Alamo bowl.