And while Cubs ace Arrieta plied his National League trade with his right hand on the North Side of Chicago and Astros left-hander Keuchel excelled in the American League deep in the heart of Texas, both young starters had something in common other than beautifully bushy beards: breakout 2015 seasons that vaulted them to the game's true elite for the first time in their careers.
Arrieta won the award over Dodgers right-hander Zack Greinke and the man who won the award in three of the previous four seasons, Dodgers lefty Clayton Kershaw.
Meanwhile, Keuchel prevailed in the AL race, besting runner-up David Price of the Toronto Blue Jays and third-place finisher Sonny Gray of the Oakland A's. Keuchel garnered 22 first-place votes to Price's eight. Chris Sale of the White Sox finished fourth, ahead of fifth-place Chris Archer of the Tampa Bay Rays.
Keuchel became the first Cy Young winner on the Astros since the club moved from the NL to the AL in 2013. Previous Astros winners in the NL were Mike Scott in 1986 and Roger Clemens in 2004.
"It's something I definitely never expected," Keuchel said. "Just playing the game is good enough for me, and just to be in the same category as Sonny and David was special in its own right. But there's a number of pitchers I look up to, and it's something that hasn't sunk in. I don't think it will for some time."
Keuchel was the only one of the three finalists to reach the exalted threshold of 20 victories, but he did a lot more than that on the statistical front. Keuchel finished 2015 with a 20-8 record, a 2.48 ERA, 216 strikeouts in an AL-high 232 innings and a 1.02 WHIP. He also didn't lose a single game at home, with a 15-0 record and 1.46 ERA at Minute Maid Park.
"I'd be lying if I said I wasn't a little anxious for the verdict," Keuchel said. "I really thought David and Sonny would be me, and that's just because I'm big fans of those guys."
But Keuchel also said it was not an individual award. He had plenty of people to thank, including his current pitching coach, Brent Strom, and a host of others dating to his college days at the University of Arkansas.
"This takes a big body of work, not just this season," Keuchel said. "But I've had to scratch and claw to make a lot of adjustments and be comfortable in my own body. There's numerous guys I've taken bits and pieces from and tried to learn from, so by no means is that all me."
Not surprisingly, the Astros and Major League Baseball were quick to react to Keuchel's big win on social media, with congratulations all over Twitter.
But while it might be unknown how Keuchel will follow up this historic season, one thing that he guaranteed was that the baseball world will see the return of his beard, which, like Keuchel, matured into excellence in 2015.
"It really has come into its own," Keuchel said.
The same was being said again and again about Arrieta, who won with 17 first-place votes, outpacing Greinke, who had 10, and Kershaw, who had three. Pirates righty Gerrit Cole finished in fourth place and Nationals righty Max Scherzer was fifth.
Arrieta became the fifth Cubs pitcher to win the Cy Young Award and the first since Greg Maddux in 1992. The other three Cubs Cy Young winners were Rick Sutcliffe (1984), Bruce Sutter (1979) and Ferguson Jenkins (1971).
"I'm a little relieved, honestly, to finally know how it played out," Arrieta said after being sprayed with champagne by his friends. "I have to say thanks to all the guys I've continued to compete against year in and year out to try to take my game to the next level. … All the hard work's been worth it."
The Cubs had a resurgent year powered by a young, exciting core. They won 97 games, took the NL Wild Card Game, and beat the first-place Cardinals in the NL Division Series before bowing out to the Mets in the NL Championship Series.
NL Rookie of the Year Kris Bryant was a big part of it, and so was NL Manager of the Year Joe Maddon. In fact, with Arrieta's win completing a trifecta of sorts on the North Side, the Cubs became the first team since the 2001 Mariners and the first NL team since the 1991 Braves to take home three BBWAA awards in the same season.
"I was really excited to see [Joe] and Kris win those awards, and to be part of that with those guys and to do what we did as an organization is really incredibly special, and it's just something that we get to continue to look to build on."
Arrieta doesn't have to do much building if he repeats what he did in 2015. He led the Majors with 22 wins, only lost six decisions and posted a 1.77 ERA that was second only to Greinke's 1.66. Arrieta's second-half ERA of 0.75 was the lowest in Major League history, and he added 236 strikeouts in 229 innings, a 0.87 WHIP, and a no-hitter over the Dodgers.
It was the culmination of a late-blooming career that began in Baltimore and has blossomed in Chicago as a result of talent, potential and a lot of hard work.
"Honestly, it took a number of adjustments for me to really get to the point where I felt like I could go out there every five days and be dominant," Arrieta said. "Some guys, it kind of clicks right away in their career. Obviously, Clayton came to the big leagues and was dominant right away and he's had a tremendous career, and the same with Zack.
"Obviously with me, it took a little bit longer, but I was able to make some adjustments necessary to have some success on a consistent basis. That's when the ball really started to roll for me.
"This award … it's been a lot of hard work, a long time coming, and a lot of adjusting, trying to figure this game out. And I'm still learning."
Doug Miller is a reporter for MLB.com. Follow him on Twitter @DougMillerMLB. This story was not subject to the approval of Major League Baseball or its clubs.