This isn't the first time Browns rookie Baker Mayfield began a season as his team's No. 2 quarterback and then quickly became a full-time starter.

When Mayfield was a junior at Lake Travis High School in Austin, Texas, the coaching staff started Collin LaGasse in the season opener because he was a popular team leader and a year older than Mayfield. But on the Cavaliers' opening possession, LaGasse suffered a separated shoulder, allowing Mayfield to take control. He led Lake Travis to a 35-7 victory over rival Austin Westlake at the University of Texas and never looked back.

"That's about as big a pressure-packed game there is for a high school quarterback," Lake Travis coach Hank Carter said recently by phone. "He's always believed in himself.

"He wasn't afraid. He would never back down from anything, and those traits have carried him through. It's a big reason why he's so successful, and I think he'll keep doing it."

Mayfield helped Lake Travis win its fifth consecutive state title during an undefeated 2011 season and went on to finish his high school career 24-2 as a starter.

He then walked on at Texas Tech, where he went 5-2 as a starter, and Oklahoma, where he finished 33-6 as a starter and won the Heisman Trophy.

He went 62-10 as a starter in high school and college combined and is now looking to go 1-0 in his NFL regular-season starting debut Sunday on the road against the Oakland Raiders.

"Having to work through the depth chart on many occasions, it’s definitely helped my story," said Mayfield, the No. 1 overall pick in April's draft. "I’ve been here before, and I’m just going to keep that same worker’s mentality."

Quarterback Tyrod Taylor started the first three games of the season for the Browns (1-1-1) but suffered a concussion last week against the New York Jets on "Thursday Night Football." Mayfield entered the game with 1:42 left in the second quarter and helped the Browns rally from a 14-0 deficit to earn a 21-17 win, their first victory since Dec. 24, 2016. He went 17-of-23 passing (73.9 percent) for 201 yards with a rating of 100.1.

"Nothing can surprise us at this point just because he's done so many awesome things as a player," Carter said. "What I [texted] him last Thursday after the game was, 'So it begins.'"

Indeed, the Mayfield era is underway. On Monday, Browns coach Hue Jackson named Mayfield the team's 30th starting quarterback since 1999.

"Now, this is the real test," Browns offensive coordinator Todd Haley said.

History won't be on Mayfield's side Sunday. Since the 1970 AFL-NFL merger, only four of the 22 quarterbacks drafted first overall have won their starting debuts, per

Mayfield hadn't taken first-team snaps in practice preceding his relief appearance against the Jets.

"It's just so hard when you don't take those reps, so his ability to come in there very poised and comfortable and go out there and play a very high-level game just shows the amount of maturity that he has," Browns cornerback TJ Carrie said. "It shows the pro attitude that he's taken since he's been here."

Now Mayfield has a week's worth of starter reps under his belt. However, there won't be an element of surprise to him playing. Jets safety Jamal Adams said during a radio interview New York was caught off guard by Mayfield because it didn't game plan for him. The Raiders (0-3), led by coach Jon Gruden and defensive coordinator Paul Guenther, will be ready.

"You better know that some of the great plays that Mayfield has made at Oklahoma and has made as a Cleveland Brown are scramble plays," Gruden said on a conference call. "He does an excellent job keeping plays alive. He has incredible vision down the field. That guy has eyes on the back of his head. You have to know that he's a great creative player."

Mayfield's attitude? Bring it on.

"They can game plan for me, but we’ve got other skill guys," he said. "We’ve got guys that are doing their jobs very well right now. My job is to get the ball in their hands, so I’m not going to be the one to run around and create all the plays. I’m just going to do my job and let them do the work."