CINCINNATI -- Reds rookie starting pitcher Luis Castillo hasn't had any easy opponents through six big league starts. The flame-throwing righty has faced only first-place teams or playoff contenders thus far -- the Nationals (twice), Brewers, Rockies and D-backs (twice).
The first encounter with Arizona yielded Castillo's first win. On Thursday, a rough first inning was followed by an important course correction, but it was too late in Cincinnati's 12-2 loss to the D-backs.
"If you're going to face these type of hitters, you have to be 100 percent ready, mentally and physically," Castillo said via translator Julio Morillo. "You know you can't make mistakes, because you know you're going to pay for it."
Castillo, gave up four earned runs and four hits over six innings with one walk and seven strikeouts. But his first three batters of the day reached safely, with bad consquences.
Following a leadoff walk to Daniel Descalso on five pitches, Chris Iannetta hit a double and Jake Lamb slugged a 0-1 changeup for a three-run home run to center field that quickly made it a 3-0 game.
After the homer, Castillo retired 12 of the next 13 and 18 of his last 20 batters. A mechanical adjustment was made after the first inning.
"He has a tendency to pull the front side," Reds manager Bryan Price said. "You can see, especially against a right-handed hitter, a lot of those fastballs he misses are glove-side misses, or to the catcher's backhand. He's really got to focus on staying in line to the plate. I think Mack [Jenkins, the pitching coach] had a good conversation with him to really get him lined back up."
"I think I was working too fast and that's why my front shoulder was open, working too fast," Castillo said. "Everything was missing arm-side. After that I just figured it out, I picked my tempo up, I knew what I had to do in order to be better. After that, everything was back to normal."
Castillo, 24, is capable of throwing 99-100 mph but reached a maximum velocity of 97.9 mph, according to Statcast™. Once he made some fixes, his changeup was more effective and unlike the first inning, he was able to strike out Lamb with it in the sixth.

"When you've got 100 like that, I'm not saying you're cheating to it, but you're looking for that heater," Lamb said. "And he was locating that changeup really well. He was throwing it down. He got me on it, full count. Situation like that, if you're going to spot up that changeup low and away -- it was actually probably just away -- for a strike, you got to give him credit. That's really good stuff."
Castillo threw 100 pitches and got through six innings, leaving with a 4-1 deficit. He is 1-3 with a 3.86 ERA since his promotion from Double-A Pensacola.
"We had to have it, we had to have the [sixth] inning even though he didn't really pitch to the top of his ability," Price said. "He did keep himself in the game for six innings and that was important considering the state of the bullpen."