The Pirates began the 2019 season with a rotation led by Jameson Taillon, Joe Musgrove, Trevor Williams and Chris Archer. It was full of experienced talent that could help a young pitcher like Mitch Keller learn about how a Major Leaguer works and handles his business.

Now Taillon and Musgrove have been traded to the Yankees and Padres, respectively. Williams was designated for assignment and signed with the Cubs. Archer went back to the Rays after his $11 million option was declined.

At only 24 years old, Keller may now be in a position to lead the Pirates’ rotation.

Manager Derek Shelton has said that leadership happens organically and can’t be forced on anyone. But after his conversations with the Pirates about his role in a new-look rotation, Keller understands what is being asked of him.

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“Just want me to be a leader, in a way, even though I'm still really young and haven't had that many years in the big leagues,” Keller said. “But they do want me to step into that leader role and be that kind of guy that people look up to and we build around."

If everything goes to plan, 2021 will be Keller’s first full Major League season, and he can finally begin to grow into that mantle. He’s already become a household name in Pittsburgh despite only throwing 69 2/3 innings, largely due to his multiyear run as the club’s top prospect.

But things didn’t naturally come easy to Keller when he arrived in the big leagues. He gave up 72 hits and 16 walks in 48 innings in his debut season en route to a 7.13 ERA. His 2.91 ERA looked great on paper last season, but it stood over only 21 2/3 innings, a span in which four of the nine hits he allowed were homers and he nearly issued a walk an inning (18 total).

Catcher Jacob Stallings said that some of the early struggles had to do with Keller implementing a new slider that still needed polishing and the general issue of inexperience, but that Keller handled it well.

“I’ve always thought that through failure is when you kind of learn the most if you approach it the right way,” Stallings said. “I think he did that.”

In another sense, though, Keller showed his stuff could play. His K/9 rate in his troublesome ‘19 season was a strong 12.19. He closed out last season with a streak of 11 hitless innings, although he allowed eight walks in five innings in his final outing, facing Cleveland.

"It gives me a lot of confidence,” Keller said of those final games. “[Pitching coach Oscar Marin] and I talked after that last game. Obviously, I don't want to have eight walks again in a game, but in a way, it gives me more confidence to know that when I was in the zone, they weren't hitting it, and I do have really good stuff.”

The rest of the Pirates have taken notice, including Steven Brault, a candidate to be the Opening Day starter. The reliever-turned-starter has seen Keller grow into a player who looks like he knows he belongs here, which is one of the big building blocks of a confident pitcher.

“Mitch is going to be one of the leaders,” Brault said. “He’s going to be a very good pitcher. We all know that. We’re excited to watch him pitch and be there with him. He seems like one of those guys who can be pretty special, so I’m excited to watch him.”

So as the Pirates progress through the 2021 season and learn who will become key members of the core they want to grow to contend for the playoffs, they'll be hoping that Keller can step up and establish himself alongside Ke’Bryan Hayes as a crucial piece of that group.

Keller will continue to reflect on the lessons of the former Pirates, lessons that will shape how he approaches the game as he tries to become the ace the organization believes he can be.

"Just working my [butt] off every day and going out there and doing things the right way, just like Jamo, Joe and Trevor and all those guys have taught me along the way here,” Keller said. “Just fall into their footsteps.”