NORMAN, Okla. (AP) Baker Mayfield arrived on Oklahoma's campus as an unpredictable gunslinger with a chip on his shoulder.
He's still an emotional sparkplug, but he has reined in his play and evolved into one of the most efficient quarterbacks in college football history.
Mayfield made his name as an underdog with something to prove. He started his college journey as a walk-on at Texas Tech, then transferred to Oklahoma and became a star. Last season, he finished fourth in Heisman Trophy balloting and led the Sooners to the College Football Playoff.
Now, after an even better season, he's bound for New York as a Heisman finalist. Though nobody is slighting him anymore, Mayfield's competitive fire has pushed him to new heights. His efficiency rating of 197.8 is the highest in FBS history, ahead of the record of 191.8 set by Russell Wilson in 2011.
''I've had a good year,'' Mayfield said. ''A lot of that is a credit to my teammates. The way we've practiced and the way we've executed every week, every day, just the way we've worked - it's shown just by our undefeated conference run.''
Mayfield still likes to have fun. He sported a horseshoe mustache during the Oklahoma State game, saying there's a new sheriff in town as a dig at the rival school's Cowboy mascot. In what amounted to the Big 12 championship game last Saturday, Mayfield wore a shirt under his uniform proclaiming the Sooners the 2016 conference champions during the game.
''Typical Baker,'' Oklahoma running back Samaje Perine said. ''There's nothing wrong with being confident, and he has all the confidence in the world. He has more confidence than he needs. It's him.''
When it's time to get serious, though, Mayfield is all business.
''He's always been coachable,'' Oklahoma offensive coordinator Lincoln Riley said. ''A lot of guys have success early. The guys that continue to improve and don't believe all the hype - they continue to work and continue to have that inner drive. He certainly has that, and that's why he's gotten better and better.''
Mayfield entered this season among the favorites to win the Heisman, but started relatively slowly, with average performances by his standards in losses to Houston and Ohio State. He came back in conference play and completed 73.5 percent of his passes with 31 touchdowns and just six interceptions for a passer rating of 208.9. He never threw more than nine incomplete passes in any Big 12 game.
Riley said Mayfield bounced back by worrying only about competing and doing his best for the team.
''When you don't look at outside stuff, your situation doesn't matter,'' Riley said. ''When you're focused on outside stuff, then you're going to be happy when people love on you and you're going to go into the tank when you lose a game like we did early in the year and everybody tells you you're terrible.''
Mayfield said dealing with the spotlight during his breakout season last year helped him handle the increased scrutiny this season.
''It happened a little earlier just because of the year I had last year, so I've been able to just relax and not worry about whatever everybody thinks and just get my guys the ball and let them shine, too,'' he said.
Fellow Heisman finalist Dede Westbrook has been shining most brightly. Last season, Sterling Shepard was Mayfield's security blanket, but with Shepard now playing in the NFL for the New York Giants, Mayfield was forced to find a new go-to receiver. Westbrook stepped up with 74 catches for 1,465 yards and 16 touchdowns.
''He just has a knack for getting open,'' Mayfield said. ''When you have a guy like that, especially with his speed, you really can't overthrow him. It's kind of a situation where you see him and he's 1-on-1 coverage, you can literally just throw it deep to him and let him go run under it.''
Westbrook, also up for numerous major awards, believes Mayfield should win the Heisman.
''I think Baker is the best quarterback and best player in the country,'' Westbrook said. ''There is no doubt about it. Whenever he's out there, it's just his mentality and the fact that nobody can stop him and he's going to dominate in every phase of the game that he possibly could.''
HEISMAN-DEFINING MOMENT: Oklahoma was coming off a loss to Ohio State and trailed TCU 7-0 early. The Sooners had the ball at the TCU 4-yard line when Mayfield faked to Perine, kept the ball and spun out of a tackle. He overpowered TCU's Niko Small at the goal line and stiff-armed him to the ground in the end zone . The offense has maintained that attitude ever since.
BEST GAME: Texas Tech quarterback Patrick Mahomes lit up the Sooners for an FBS-record 819 total yards, including 734 passing, but Mayfield was up to the challenge. He completed 27 of 36 passes for 545 yards with seven touchdowns and no interceptions and led the Sooners to a 66-59 win .
WORST GAME: Completed 17 of 32 passes for 226 yards, with two touchdowns and two interceptions in a 45-24 loss to Ohio State .
PRO PROSPECTS: Mayfield has said he will return for his senior season , and he will have a chance to boost his NFL stock. He is a bit short at 6-foot-1, but players like Wilson have paved the way for him to get a look.
''I think he's got a chance to be a great pro,'' Riley said. ''What the guy is doing right now and the level he's playing at right now - not many people ever play at that level.''
Follow Cliff Brunt on Twitter: www.twitter.com/CliffBruntAP .