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Castillo was born in Baní, about an hour southwest from Martinez’s hometown of Manoguayabo, and years ago he started watching old Martinez starts on YouTube as a part of his pregame preparation. Castillo wants to remind himself before every start to emulate the way Martinez carried himself on the mound.

“[He] was always competing, never giving up no matter what the situation was,” Castillo told Sporting News. “I study his pitching a lot, and he seems to me like every time he came and pitched in the big leagues, year by year, he comes with more mound presence, more confidence in himself, so I tried to copy that.”

Watching Martinez every five days helps to remind Castillo that every pitch, every inning and every batter is a battle he needs to win. Tucker Barnhart, who has caught most of Castillo’s starts not only this season but since he came up two seasons ago, saw right away the supreme mound presence Castillo had, even as a rookie.

Barnhart made his debut with Cincinnati in 2014, when he was catching a staff of Bronson Arroyo, Johnny Cueto, Mike Leake and Homer Bailey. Guys who had been there, done that already. They had seen any sort of scenario possible on a baseball field and carried themselves accordingly. Surprisingly, Barnhart said, Castillo was the same way from the moment he came up.

“For a guy that hasn’t been in those situations at all at the big league level to be able to just basically roll out of bed and be that way was really cool,” Barnhart said. “The one thing for me that’s always been extremely impressive about Luis is that nothing seems to really rattle him. That’s kind of stayed constant from the moment he got to the big leagues.

“He just seems to say, ‘The hell with it, I’m going to get the next guy.’ It’s really impressive and it’s really fun to catch.”

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This season, Castillo is using that confidence to put together a Cy Young-caliber season. Through his first 13 starts, he has a 2.38 ERA and 90 strikeouts in 75.2 innings. His strikeout rate is way up from 2018 and his ERA way down, and this is without a significant change to his mechanics or approach. Castillo’s pitch mix is tweaked from last year, a change that’s also at least partially due to greater self-confidence.

In 2018, Castillo used his changeup about 26 percent of the time, and so far this season he’s upped that to nearly 31 percent.

“That has been my pitch since I came up,” Castillo said. “That’s my best pitch. And I just, I don’t know, I just feel better throwing it down in the zone or more often, and it’s been working fine.”

His changeup has a slightly higher whiff rate this year, up to about 29 percent from 26.8 percent a season ago. And opposing hitters, who have never done well against Castillo’s best pitch — they batted just .198 against it in 2018 — are doing even worse than before. So far this season, they’re managing a meager .145.

“It gives guys another thing they have to worry about. He’s been able to pitch up in the zone more than he has in the past,” Barnhart said. “Using it more in fastball counts, which makes it even more difficult for guys to pigeon-hole him into a fastball.”

Castillo’s slider has gotten better and his command of his fastball has developed as well, Barnhart said. As a result, he’s been able to tweak how he uses his other pitches as well. For instance, he’s more comfortable working higher in the zone. In 2018, Castillo threw 62 pitches, or about 2.2 percent of the total he threw for the year, in the area just above the strike zone, according to Statcast. This year, that’s up to 6.6 percent. It’s still a relatively small difference, but it matters because it affects how hitters have to gameplan. They are less able to eliminate an area of the zone when he’s more willing to put his pitches there.

“Last year, we were using the fastball up but not as much as this year,” Castillo said. “Having different spots in the zone where you can make your pitches better makes you better.”

It’s also helped that Castillo has a full year of experience. He took some lumps in 2018, sure, but there’s a lot to be said for getting to run the course of a full season in the majors. Players get a chance to see more of what baseball might throw at them and learn how they have to respond.

“It helps a lot having the experience I had last year, pitching all year here in the big leagues, and it makes it easier for me because you can know more of who you’re facing,” Castillo said. “And that prepares you better to come this year and do the job that I’m doing.”

Castillo will have some competition for the Cy Young in the National League — the Dodgers’ Hyun-Jin Ryu has one of the strongest cases so far — but there’s no doubting his growth as a pitcher. Castillo is the ace of a staff that added veterans Sonny Gray and Tanner Roark to the mix, but it’s not just because of his performance. Castillo’s confidence, learned in part from watching Martinez on YouTube, carries weight with the other pitchers in Cincinnati. When asked where his strong sense of mound presence comes from, reliever Robert Stephenson couldn’t help but chime in from his locker.

“Tell him because you’re nasty,” Stephenson said.