NORMAN, Okla. (AP) — Lincoln Riley barely looks older than some of his players.

Don't let it fool you. Oklahoma's 32-year-old offensive coordinator is the mastermind behind the Sooners' offensive resurgence and quarterback Baker Mayfield's standout statistics. His powerful offense will be on display when No. 4 Oklahoma faces No. 1 Clemson in a New Year's Eve in a semifinal on the road to what the Sooners hope will be their eighth national title.

Coach Bob Stoops' proud program was reeling after a 40-6 loss to Clemson in last year's Russell Athletic Bowl, so he took a chance on East Carolina's young offensive coordinator. The Pirates had set numerous school records with Riley's version of the Air Raid, the same system that lifted Oklahoma back to national prominence the previous decade.

Stoops' directive to Riley was to move forward, but bring back the old results.

After a few bumps in the road, Riley has delivered. Oklahoma ranks third nationally with 45.8 points per game and seventh with 542.9 yards.

"Lincoln is a very innovative and bright coach," defensive coordinator Mike Stoops said. "It didn't surprise me — I knew in the spring. It took a while to get adjusted to our personnel. Our running backs are different than what he's used to dealing with. Once he got those guys in position to do what they do along with Baker and the great wideouts — I think we have all-out confidence in his ability."

Riley said figuring out the personalities on his team was the biggest challenge.

"It's just learning our guys," he said. "Trying to learn what makes them tick, what makes them go, what we're not good at and need to cover up and what we are good at. Just our staff, continuing to jell — I think we have, really, really well."

At first, the Sooners were one-dimensional, even with a pair of talented backs. Samaje Perine had a huge freshman season last year and Joe Mixon was one of the nation's best high school backs two years ago, but the offensive line's three new starters slowed the process. The Sooners hit a low when they ran for 67 yards on 37 carries in a 24-17 loss to Texas.

Even as the Sooners struggled, Riley often said the team was just a step away from busting long runs. Last season, after Oklahoma's loss to TCU, The Sooners fell apart under the weight of disappointment, injuries and the inability to deal with high expectations. This year, the Sooners say Riley helped them bounce back.

"Coach Riley came in and talked about the mentality and mentality means everything," receiver Sterling Shepard said. "I look back last year and I see that, and then I look at this year and I see that."

The improved mentality showed most in the running game. After the Texas loss, the Sooners averaged 299.9 yards rushing in their next seven games, all wins. Riley's offenses at East Carolina ran for at least 230 yards five times in 64 games from 2010-2014. The Sooners have done that in seven straight games this season.

"He came in here, and it's kind of different personnel," Mayfield said. "He's adapted to it. I appreciate the way he's handled it. We have running backs that no one else has. He's adapted to that, and to our personnel very well, and he handles it. We're seeing as we go along — it's getting better and better with our matchups. I'm comfortable with it."

Earlier in his career, Riley was an assistant at Texas Tech under Mike Leach, who turned the Air Raid into an offensive onslaught with the Red Raiders. The way Riley fixed Oklahoma's problems on the fly impressed Mike Stoops.

"How quickly he learned was probably the most impressive part of him," he said. "And how not stubborn he is. That says a lot about how great a coach he is. He's willing to adjust and adapt. I think that's what all great coaches do."

As the team's fortunes have changed, Riley has remained steady.

"Coach Riley is a guy that's the same every single day," backup quarterback Trevor Knight said. "He always brings an intensity and a passion. He doesn't get too high and he doesn't get too low. His leadership has been crucial in the success that we've had this year."

He also doesn't change how he interacts with his players.

"He knows he can push me," Mayfield said. "I like being pushed. It's a challenge. I want to get better. He's doing that every day in practice."

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Follow Cliff Brunt on Twitter: @CliffBruntAP