BRADENTON, Fla. -- Each of the last two years, Mitch Keller has pitched in Minor League championship series. Last October and November, he dominated Arizona Fall League lineups loaded with top prospects. But on Sunday afternoon, in a game with relatively low stakes, Keller was nervous.
"It's kind of a big deal," he said. "I kind of knew that going in, it was my chance to show people what I can do."
Keller warmed up in the Pirates' bullpen, preparing for his first relief appearance of any kind since he was in Rookie ball. He heard the buzz emanating from the crowd of 7,035 as he trotted in to pitch the seventh inning. He was anxious. Then Keller, 21, provided a glimpse of his potential on the mound as he struck out three Red Sox over two scoreless innings in his big league Spring Training debut.
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Wearing a No. 94 jersey with no name on the back, Keller joined several Minor League teammates on the van ride from Minor League camp at Pirate City to LECOM Park on Sunday morning. There, he caught up with outfielder Jordan Luplow and others in the big league clubhouse. After watching Tyler Glasnow, Brett McKinney and Dovydas Neverauskas pitch, Keller took his turn.
"Once I got the first strike over, I settled down a lot," he said. "That felt really good. I was very happy with how it went."
Keller used his full arsenal of fastballs ranging from 94-97 mph, curveballs and changeups to strike out Rusney Castillo and Ivan De Jesus Jr. in a perfect seventh inning. He gave up a two-out double in the eighth, then fired a 95-mph fastball that Luke Tendler tipped back into catcher Jacob Stallings' glove for strike three.

"It's always good to see one of our young men that's having success, that's growing, that's developing well to come out and perform in this arena as well," manager Clint Hurdle said. "There was nothing to be disappointed about today."
A second-round Draft pick in 2014, Keller has given the Pirates no reason for disappointment throughout his young career. He owns a career 2.79 ERA and a 1.05 WHIP in the Minors. He advanced last year to Double-A Altoona, where he will begin this season, and eventually started their Eastern League championship-clinching victory.
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MLB Pipeline rates the right-hander as the Bucs' top prospect and the game's No. 15 overall. He already possesses an effortless delivery that prompted him to remind reporters, with a laugh, "I mean, I'm trying." He said his changeup, the third pitch he needs to succeed at higher levels, is "coming along nicely." The tips he receives from more experienced pitchers, including Jameson Taillon, are more about the mental side of the game.
"Just little things, like, really make sure you're trying to nail every pitch and be focused on every one," Keller said, "because when you get to the big leagues, you have to be."
Keller was admittedly disappointed he didn't receive an invitation to big league Spring Training. But he could reach the Majors later this year or, more likely, join Pittsburgh's rotation in 2019. Sunday afternoon was only the first taste of what awaits him.
"I'm not trying to get too far ahead. But it's close," he said. "Just talking with people, I'm right there, so I just got to hone in my craft and just get everything a little bit better than it already is and be more consistent, so that's really what I'm looking for."