For his first Cactus League start of 2021, it was mostly a smooth evening for Reds pitcher Luis Castillo against the Mariners on Friday. Castillo worked two scoreless innings with one walk and one strikeout.

“It felt like the locations of the pitches were really good,” Castillo said through translator Jorge Merlos. “Some of the off-speed [pitches] stayed over the plate, but that’s why it’s the first start of Spring Training. We’ll keep working on it through the spring.”

On Monday during a ‘B’ game, Castillo also worked two scoreless innings. The right-hander is a little behind other Reds pitchers in camp because he was a late arrival after having travel issues leaving his home in the Dominican Republic.

Castillo, 28, was 4-6 with a 3.21 ERA over 12 starts last season, including 4-1 with a 2.20 ERA in his final five starts.

Known for his spectacular changeup that records the majority of his strikeouts, Castillo said that he used the pitch at one point four consecutive times vs. a hitter Friday.

“The changeup is not 100 percent perfect at the moment, but that’s why we worked on it today,” Castillo said.

Seeking to get hitters off of his fastball and changeup, Castillo has wanted to improve his slider. According to Statcast, he used it 17.7 percent of the time in 2020 -- consistent with his career numbers.

The slider only got limited use vs. Seattle.

“I only brought it out once and it didn’t turn out for a strike, so I kept it in my back pocket,” Castillo said. “I’ve been working on it a lot during the bullpen session. It’s still there.

“As we’re working on it, we’ll have a better confidence in using that pitch as the season goes on. That’s the plan for now.”