(CBS) Touted White Sox pitching prospect Michael Kopech had a pretty good idea of when professional baseball might be in his future.

It was shortly after he was in his early teenage years and throwing smoke.

“When I was probably 14 years old, I hit 90 for the first time,” Kopech said in an interview with Dan Bernstein and Jason Goff on 670 The Score on Wednesday afternoon. “At the time, I didn’t even realize the significance of that. But you know, once that happened, I kind of just stuck with it. That’s what I enjoy the most, is throwing the ball hard.”

The 21-year-old Kopech recently finished a stellar debut season in the White Sox organization. Acquired in the Chris Sale trade with the Red Sox last December, Kopech went 8-7 with a 2.87 ERA, 1.15 WHIP and 155 strikeouts in 119 1/3 innings at Double-A Birmingham. He was promoted to Triple-A Charlotte in August and went 1-1 with a 3.00 ERA in 15 innings there.

Kopech cited the biggest challenge for him as he’s advanced levels is using his entire arsenal to get ahead in the count instead of just relying on his fastball initially and then turning to his breaking ball.

“I recently had to start working on pitching more so than throwing hard obviously,” Kopech said.

“You hear once you get into professional baseball from the very beginning that big leaguers can hit fastballs. And you’re like, ‘Ah, sure they can.’ Then you start to work up the levels, and you still kind of get away with it. And out of nowhere, I get to Triple-A, and these guys can hit fastballs. It wasn’t just a joke. They can hit. I had to start thinking a little bit more. It made the game a little more challenging, but I love the challenge. It made me feel more like I was playing a game of chess instead of just trying to blow the doors off somebody.”

The White Sox have made clear they’ll give Kopech the opportunity to win a starting rotation spot out of spring training in 2018.

“He’s shown the ability at whatever level he’s pitched at to take the challenge and run with it,” amateur scouting director Nick Hostetler said recently. “He’s done that. He’s showing maturity beyond his years, work ethic, everything you want out of a guy that you want to be competing for a spot next spring training. I think he has not only the physical talent but the mental capabilities to do it. I fully expect him to compete for one next year.”

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