There was a lineage developing in the Pittsburgh Pirates’ starting rotation, and it wasn’t good — not for the Pirates, at least. Charlie Morton, Gerrit Cole, Joe Musgrove, Tyler Glasnow: Between Pittsburgh’s most recent postseason run in 2015 and 2021, a veritable All-Star rotation’s worth of pitchers spent early-career time with the Pirates but reached their full potential only after departing for new teams.

For a while, it looked like Mitch Keller might require the same greener pastures to flourish. A consensus top-20 prospect in baseball ahead of his 2019 debut, the sturdy, 6-foot-2 right-hander got blasted in his first forays in the majors. Over 170 1/3 innings from 2019 to 2021, he allowed a 6.02 ERA while leaning on the four-seam fastball and curveball that won games and earned plaudits in the minors.

Something had to change.

“I think the game just told me a lot of what I needed to do,” Keller told Yahoo Sports this month, “and obviously, my four-seam — what I had wasn't working.”

Unlike all those other pitchers, though, Keller didn’t need to leave Pittsburgh to change that. A new front office helmed by former Boston Red Sox GM Ben Cherington took over ahead of the 2020 season, installing Derek Shelton as manager and Oscar Marin as pitching coach. Keller — and the Pirates as a whole — didn’t find success right away, but they started to break out of the old ruts that had set the organization back. One-size-fits-all pitching philosophies went out the window. New ideas from savvy baseball minds were welcomed in, even if those minds weren’t on the Pittsburgh payroll.

Keller now looks to be the end of that unfortunate lineage and perhaps the beginning of a new, brighter one. Now 27, he’s sporting one of MLB’s 10 best ERAs heading into his 10th start of the season Sunday against the Arizona Diamondbacks. His past two starts have trumpeted his arrival. First, he fired his first complete game (a shutout, for good measure) against the Colorado Rockies, then he logged a career-high 13 strikeouts across seven shutout innings against the Baltimore Orioles.

Even as the young Pirates cool down after a hot start to 2023, Keller is providing reason for lasting optimism that pitchers can develop into stars in Pittsburgh, that the organization will turn over every rock looking for a winning formula.

Keller open-minded in pursuit of success

The big leagues, Shelton is quick to remind you, are hard.

“The thing that I appreciate about Mitch is he's come to the big leagues, and he's had his bumps and bruises, but along the way — and I think we think about this organizationally, we're always trying to get better — he never took the mindset of like, ‘OK, hey, I failed,’” the manager said. “He's always taken the mindset of, ‘OK, what's the next step? What can I do to get better?’”

Keller’s first step came when he sought some outside assistance at the behest of former Pirates reliever Clay Holmes.

“I was just kind of struggling, going through it,” Keller said. “And he kind of saw some mechanical things that I was doing differently, but he didn't want to say anything because he didn't want to be the one to, like, tell me I was doing something wrong or not well.”

The day after his rough 2021 season ended, Keller sought out Tread Athletics, one of several private performance gyms that have become breeding grounds for pitching innovation.

The late 2010s Pirates’ pitching woes were broadly viewed as a problem of holding on to an approach that once worked — Ray Searage’s focus on sinkers and groundballs — too tightly and for too long. The new Pirates leadership has cast a wider net, openly encouraging pitchers to work with Tread, where Shelton said Marin & Co. have a strong working relationship with the instructors.

“So if we can learn from each other, it's really important,” Shelton said. “And I think it would be foolish of us to not be willing to listen to people that have specialties in certain areas and then apply it.”

So yes, Keller has seen more technology in the mix and more emphasis on pitch design — trends across just about every organization. He has also noted a shift in the way the Pirates steer pitchers toward their future forms.

“I also think our mentality has changed on what we need to do as pitchers,” he said. “I think the big thing, actually, is identifying what we're really good at — what we're personally good at. And that has helped development a lot, I think, throughout the minor leagues and throughout the big leagues.”

Shelton calls this “organizational alignment” in the pitching department. And there are wins piling up around Keller. Veterans Tyler Anderson and Jose Quintana found improvement in Pittsburgh in recent years. This year, Vince Velasquez was experiencing newfound excellence by accentuating his slider, his strength. Younger, potentially foundational arms such as Roansy Contreras and Johan Oviedo are attempting to follow their own versions of that track, homing in on their best pitches, even when that’s not a traditional fastball.

Lots of pitches lead to lots of confidence

The abilities Keller discovered in himself weren’t so much oriented around one underused pitch as they were about the dexterity to quickly pick up and command multiple weapons.

“I have an arsenal for righties and lefties, and just being able to command all of them at any given time is definitely a huge, huge strength of mine,” Keller said. “I would say the strength for me is probably the sinker, the sweeper — and the cutter to lefties has been huge for me, too.”

Meet the new pitches. Between that low moment in 2021 and the start of 2023, Keller added all three of those offerings, roughly doubling the size of 2019 Mitch Keller’s arsenal of pitches.

In 2021, he was throwing his four-seam fastball about 57% of the time and complementing it with a slider he threw 24% of the time and a curveball he whipped out almost 15% of the time, plus a sparingly used changeup.

In 2023, he wields a menagerie of offerings that now includes the sinker, the cutter and the sweeper (an en vogue slider offshoot with more horizontal movement) where his slider used to be. If you look at his overall pitch usage, it looks sprawling — his four-seam, sinker and cutter are used in almost identical portions — but it’s not variety for variety’s sake. Keller’s many options are tailored to and targeted for the hitters he’s attacking.

For instance, right-handers mostly see the sinker, which veers hard toward them as it approaches the plate, and the sweeper that works off the same plane but takes a hard turn in the opposite direction. Keller will also throw the cutter, essentially a tightly wound slider that darts down and to the glove side, low and outside.

Lefties, the batters who traditionally pose a greater threat to a right-hander such as Keller, get a mix of the straight, gravity-defying four-seam and the cutter in a different location, higher so it mimics the four-seam’s path right up until it doesn’t, plus the roller-coaster curveball.

Adding the sinker and cutter produced obvious improvement in 2022. Through Keller’s first nine starts with all of the gains fully operational, he’s running career-best numbers in virtually every statistical column. And even advanced metrics such as DRA, from Baseball Prospectus, view Keller’s work so far this season as elite, backing up his shiny ERA.

Shelton, the manager who has watched Keller grow into a top-of-the-rotation hoss who has reportedly begun talks about a long-term extension, applauded Keller’s mental and emotional growth as a player, citing his cool reaction to an Opening Day jam against the Cincinnati Reds.

“Before, there would have been like, ‘Oh, what am I going to do to execute?’” Shelton said, recalling that Keller escaped having allowed only one run. “Now it's the sense of like, ‘OK, I have a plan in place.’”

The plan is working for Keller and growing more solid with every outing.

“You can't just go out there and magically have confidence,” he said. “It stems from everyone around you and a few good things happening and just kind of letting it accumulate that way.”