The line for Chapman was one scoreless inning with one hit, one hit batsman and two strikeouts. He threw 17 pitches, 12 for strikes, and twice reached 97 mph with his fastball.
"I saw a guy that was around the plate with three pitches, and his arm looks live," Reds pitching coach Bryan Price said. "He's athletic around the mound. I wasn't disappointed in any way."
In relief of Homer Bailey, Chapman began the second inning and started off by getting Wladimir Balentien to ground out on his third pitch. Yonder Alonso hit a double to the left-field corner, leading to Chapman working from the stretch.
His first mistake was a painful one for Todd Frazier. Chapman hit Frazier in the right knee with a 95-mph fastball and he crumpled to the dirt. After several moments, Frazier was helped off of the field and he would later be diagnosed with a bruised right quadriceps. X-rays weren't needed and he will be evaluated again on Friday.
"I was trying to throw the ball inside. There was nothing intentional," Chapman said. "I wasn't scared at all, but it's not something I wanted to do to a teammate."
Chapman escaped the jam when he fired a 97-mph heater to strike out Ryan Hanigan swinging. Next batter Wilkin Castillo saw a couple of fastballs, broke his bat when he fouled off an 85-mph slider and swung and missed on a perfectly thrown 82 mph changeup.
"I had no chance," Castillo said of the final pitch. "He threw hard and was sneaky, too."
Before Chapman came to camp, his detractors cited the lack of a quality changeup in his repertoire. But it's been one of his best pitches during bullpen sessions and live batting practice.
"I feel really good about the changeup," Chapman said. "I'm working really hard on it and I think it's going to get better."
And with that last changeup to Castillo, Chapman's first game-like experience was finished.
"Chapman threw the ball great," Reds manager Dusty Baker said. "The ball was over the plate and it was live. If he gets that ball over the plate, he's going to be hard to hit. But he did keep the ball down, which is a big plus."
"He was overthrowing a little bit, maybe," catcher Ramon Hernandez said. "Remember, he hasn't pitched in eight months. He's trying to get a rhythm. He fixes that up, he'll be set. He really pitched well. He threw a lot of the fastball and found the strike zone with it."
The scenario on Monday vs. Kansas City will be similar to what went down on Thursday. Bailey will start the game for Cincinnati, with Chapman expected to come out of the bullpen.
"Down here it doesn't matter. One thing at a time," Baker said Thursday morning of the decision not to start Chapman.
"Plus if we pitch him later, fans will stick around and drink more beer," Baker joked. "You didn't know I was in marketing, did you?"
Chapman was one of the most ballyhooed additions to the Reds in recent history. In January, the club invested $30.25 million over six years to sign the 22-year-old, who defected from Cuba last summer.
Despite having no professional experience outside of pitching in Cuba, Chapman is making a bid to join the Reds' rotation as the fifth starter. He is competing against Micah Owings, Justin Lehr, Matt Maloney, Travis Wood, Mike Lincoln and Kip Wells.
"I thought it wouldn't go as well as it has," Chapman said of his camp performance to this point. "But I've worked hard on my control and command, and it's working out very well."