The slider hasn't been part of Luis Castillo's repertoire for long, but it's already becoming one of his most effective pitches.
The fifth-ranked Reds prospect struck out a career-high 13 while allowing two hits and a walk over eight innings in Double-A Pensacola's 5-0 win over Mississippi on Tuesday at Blue Wahoos Stadium.
"He was mixing the location with his fastball," Pensacola pitching coach Danny Darwin said. "He moved it in and out well and was able to throw his changeup, even behind in the count, and showed a good slider with depth. He was just getting ahead of the hitters all night."
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The 24-year-old right-hander recorded three strikeouts as he retired the first six batters, but Dylan Moore led off the third with a single and reached third on a balk and a wild pitch before Castillo struck out Luis Valenzuela on a foul tip.
"I've always said that somewhere along the first couple of innings, you need to find yourself," Darwin said. "He was able to get a couple of punchouts on changeups and sliders, and the biggest thing was he had three pitches tonight.
"In the past, he'd have the slider or he wouldn't have it, and other teams would have eliminated one of these pitches, so he became a two-pitch pitcher. Tonight, he had all three working."
From there, the Dominican Republic native cruised, allowing only a leadoff single in the sixth to Connor Lien and a walk to Moore in the eighth before he fanned pinch-hitter Jared James looking for his final strikeout.
Video: Pensacola's Castillo notches 13th strikeout
"The main thing I look for is if he's getting on top of his slider, that's his biggest asset," Darwin said. "That's something he's only been throwing since Spring Training, so we've worked really hard on it on the side."
Castillo (4-3), who is in his first season with the Reds organization after being acquired from the Marlins for Dan Straily in January, has a 2.68 ERA in 13 starts, yielding two runs or fewer in nine of those outings.
"He's got a plus fastball, he's got a plus changeup," Darwin said. "And now his slider is coming each and every start. It's getting better and better.
"What I was told was [Miami] didn't think he could start over there, so he's been working on that pitch since Spring Training and he's been working really hard. He's a great kid. He respects what you try to tell him. He's out there to win and he's worked his tail off to get to where he's at."
Alex Powers struck out the side after a leadoff single in the ninth to complete the shutout.
Eric Jagielo belted a two-run homer, his fifth of the season, in the seventh for the Blue Wahoos.