He stared down "The Black Hole" in Oakland in his first start.
Yet nothing will compare to what awaits him on Sunday: Mayfield will encounter what has been an NFL rookie quarterback's worst nightmare -- the Baltimore Ravens' defense.
Under coach John Harbaugh, the Ravens have recorded the best passer rating (59.6) and produced the most interceptions (27) against first-year passers. Their 15-5 record against rookie quarterbacks since 2008 is second only to the Pittsburgh Steelers, who are 17-3.
"We do play rookie quarterbacks at a high level because it’s a transition," safety Eric Weddle said. "No disrespect to other teams, but our defense is different than other defenses. We do things that most defenses don’t do."
Does that mean a variety of different looks and blitz packages?
"I don’t know. That could be interpreted any way you want," Weddle said with a smile. "It’s not out of the realm that he could have success against us. But if we go out and play solid defense, do our job and play the way we play, then yeah, it should be hard on a rookie quarterback. That’s why they're rookies."
Here is a summary of the Ravens' domination in their 20 games against rookie quarterbacks since 2008:
Thirteen have been held under 200 yards passing
Nine have failed to complete over half of their passes
Eight have thrown multiple interceptions
Only one has thrown multiple touchdowns (Dallas' Dak Prescott)
Baltimore has beaten high-profile rookies over the years, from first-year sensations such as Andrew Luck and Carson Wentz to a future Pro Bowl player in Andy Dalton and a starter for one of the top teams in the NFL right now in Blake Bortles.
But Baltimore didn't talk about any of them with the same type of reverence as Mayfield. Ravens defensive coordinator Don "Wink" Martindale called Mayfield this generation's Brett Favre and John Elway.
This type of praise toward Mayfield continued in the Ravens' locker room.
"With a rookie quarterback going against kind of a veteran defense, you want to confuse, do different stuff, but Baker is a little different," safety Tony Jefferson said. "I’m not being biased because he’s from Oklahoma, but he does have that effect on defenses, where he’s not afraid to throw the ball in there. He’ll fire it in there. He’s not really hesitant, so we’re preparing for him like we do with any other quarterback."
The Ravens have gained the same respect in Cleveland. The Baltimore defense is ranked No. 2 overall, No. 4 against the pass and No. 2 on third downs.
Browns coach Hue Jackson, who spent two years on the Ravens' staff (2008-09) and has played Baltimore's defense over the years, has filled in the No. 1 overall pick on what to expect.
"They set the tone," Mayfield said. "He talked about how they’re the leader of the team, how they want to take control of the game [and] they want to be physical. I think he just spread the message on what their mindset is, what their mentality is, and that’s important for us to realize that."
Rookie quarterbacks' average completion percentage against Baltimore is 52.7 percent. The Ravens have allowed only 14 completions of 30 or more yards in 20 games.
Rookies just aren't given time to look downfield for an open receiver. The Ravens have sacked first-year quarterbacks a total of 52 times.
Even so, Ravens linebacker Terrell Suggs has quickly struck up an admiration for Mayfield.
"I like him," Suggs said. "I like his swag, his edginess. As a fellow competitor, you have to respect that. I like his game and his fieriness -- if that’s a word."
Mayfield is looking to do something that never has been accomplished: beat Harbaugh and the Ravens as a rookie quarterback for the Browns.
Since 2008, Cleveland rookie quarterbacks are 0-7 against the Ravens. Colt McCoy, Brandon Weeden (twice), Connor Shaw, Cody Kessler and DeShone Kizer (twice) have combined for one touchdown and 12 interceptions against Baltimore.
"We’re playing, arguably, one of the best defenses in football," Jackson said. "So, I’m sure they’re a very confident group about playing a rookie quarterback. Here, [Mayfield] is just going into his second start. He’s going to learn a lot in this game."