After his last home start of the year on Sep. 24, Diamondbacks starting pitcher Merrill Kelly had already thrown an impressive 189.2 innings this season. And he was hellbent on reaching 200.

“It’s pretty important to me, to be honest with you,” Kelly said. “You guys have heard me talk for four years now on what I pride myself on as far as being a starting pitcher, and that’s definitely eating as many innings as I can.”

Throughout his Diamondbacks’ career, Kelly has done exactly that. Since signing with the team before the 2019 season, Kelly leads all Diamondbacks pitchers with 573 innings pitched. Despite having thoracic outlet surgery in 2020, he has only missed a handful of starts along the way.

Granted, the innings-eater label isn’t a sexy one. Longtime Cincinnati Reds starter Bronson Arroyo threw 199 or more innings every year for nearly a decade and went his entire career without a top-10 finish in Cy Young voting.

Innings are valuable, though — especially for a Diamondbacks team that has lacked adequate starting pitching depth for several years. Kelly’s 4.27 ERA from 2019-21 did not jump off the page — in fact, it was almost exactly league-average — but his dependability did. That is why, entering this year, he was already the best free agent signing of general manager Mike Hazen’s tenure.

In 2022, however, Kelly reached another level. He not only reached his goal of 200 innings, but he finished the year 13-8 with a 3.37 ERA, 1.14 WHIP and .226 opponent batting average. He was more than just Merrill the Mainstay. He is Merrill the Menace. Er, Merrill the Magistrate? (I’m accepting suggestions in the comments.)

Whatever you want to call him, the D-backs’ righty is in good company. In 2022, he was one of only seven pitchers in baseball with 200 or more innings pitched and an ERA below 3.50, joining Sandy Alcantara, Aaron Nola, Miles Mikolas, Corbin Burnes, Framber Valdez and Shane Bieber. In Diamondbacks history, Kelly is just the ninth pitcher to accomplish the feat.

Reaching the 200-inning mark in 2022 is much different than in, say, 2005. In 2022, with MLB managers playing it safe with their pitchers more than ever, the 200-inning club is an exclusive one. It has only eight members. In 2005, it had 50. For Kelly, the near extinction of the 200-inning pitcher just makes being one that much more meaningful.

“That 200-inning mark is a big one for starting pitching, especially nowadays,” Kelly said. “Guys don’t hit it like they used to. It kind of used to be somewhat of a normal thing, and I feel like in this day and age, with the way bullpens are and the way pitch counts and starting pitchers are handled, not as many guys get to it.”

Undoubtedly, 200 innings is a remarkable achievement. For the Diamondbacks, however, the most meaningful development of Kelly’s 2022 season arguably had less to do with the number of innings than the quality of those innings. Excluding his abbreviated 2020 season, Kelly had career bests in ERA, ERA+, FIP, xFIP, WHIP and opponent batting average.

A cursory glance at Kelly’s peripherals makes it difficult to pinpoint why he was so much better. His strikeout rate was only slightly higher than his career norm. His walk rate was actually a touch higher. His ground-ball rate was essentially unchanged.

The key was probably Kelly’s 28.5 percent hard-hit rate, which was the lowest of his career by a wide margin. With weaker contact came fewer hits on balls in play. He also allowed just 21 homers, more than half of which came in September. Continuing to limit the long ball will be crucial for his success in 2023.

Early in the season, Kelly’s improvement was primarily due to a revamped changeup, a pitch he focused on last winter. However, based on run value, Kelly’s cutter — which is arguably the best cutter on the roster — was his most effective offering by season’s end.

Merrill Kelly, Painted Front Door Two Seamer and Back Door Cutter. 🖌️🎨 pic.twitter.com/eT6vUIpaR5

— Rob Friedman (@PitchingNinja) August 11, 2022

For Kelly, however, his success in 2022 is less about the pitches he is throwing and more about his conviction throwing them.

“The biggest thing I’ve said all year is just mindset,” Kelly said. “Being my fourth year in the league, being my fourth year on the team, I don’t put the big leagues on a pedestal anymore.”

Kelly’s journey to the majors was not a conventional one. After stalling out in the upper levels of the Tampa Bay Rays’ farm system in 2014, the Scottsdale Desert Mountain High School product pitched in the Korean Baseball Organization from 2015-18 before returning to America to pitch for the Diamondbacks. He made his big-league debut at the age of 30. Looking back on it, he admits he was starry-eyed.

“When I made my debut in [2019], you probably wouldn’t have been able to tell the difference if I was 22 or 30, the way I walked around here with how big my eyes were.”

Kelly has grown up since.

“Now it’s just more comfortability and confidence, knowing that I’ve faced pretty much anybody and everything that there is to face,” he said. “I’m in a pretty good spot now where I know if I make quality pitches just like anybody else, the results are probably going to be in my favor.”

The Diamondbacks have had many pleasant surprises in 2022, but Kelly’s evolution as a frontline starting pitcher is arguably the most significant. The team’s starting rotation has been shaky at best and atrocious at worst since 2019. Kelly could be a formidable presence alongside Zac Gallen for years to come.

Kelly would have been a free agent this winter were it not for the two-year, $18 million extension he signed before the 2022 season began. That deal, which also includes a team option, could keep him in Arizona through 2025.

With Gallen also under control through 2025, the Diamondbacks have what many teams covet: an affordable, competitive one-two punch with three years of team control. Gallen and Kelly won’t bring a division title to the desert on their own, but they could be the building blocks of the next great Diamondbacks pitching staff.

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Top photo: Kirby Lee/USA TODAY Sports