Pitching just his second professional game in the United States, Chapman struggled with his control in a 28-pitch first inning. But he collected himself and ended up allowing one run on just one hit over five innings in Louisville's 3-1 loss to the Columbus Clippers.
The 22-year-old left-hander walked two of the first three batters and went to three-ball counts to each of the first four.
"I was really wild in the beginning," Chapman said through an interpreter. "I don't feel happy with what happened today, mainly because we lost."
His early command trouble is partially attributable to excitement over his first start at home, said Bats pitching coach Ted Power.
"I think he was amped up," he admitted. "All the media, all the fans, all the attention to his first start in Louisville [had an effect on him]. He's a young guy just getting his feet wet."
Trevor Crowe walked to open the game but was erased on a forceout by Jason Donald. Carlos Santana, MLB.com's No. 11 prospect, also walked, and Donald stole third before reigning International League MVP Shelley Duncan lifted a sacrifice fly to left field.
"It was interesting to see him deal with not having his best stuff," Louisville manager Rick Sweet told MLB.com. "He worked slower early in the game. There's no doubt he's special. he just needs to learn to command his stuff."
Chapman showed just how special he is by reaching 101 and 102 mph on the radar guy. He threw consistently in the 94-97 mph range.
"I notice that I'm throwing hard when I heard the crowd gasping," the Cuban defector said. "I know that not everybody can throw that hard."
While the crowd may have been impressed with Chapman's fastball, he effectively mixed in his off-speed pitches. His changeup has been a something of a focal point in Chapman's development, and the Bats coaching staff was pleased with the way he threw it Saturday.
"I thought his changeup was much better," Sweet said. "He didn't have his command, but he didn't get frustrated. His slider wasn't as good, so he made adjustments. It was a very positive day. I see a lot of progress."
"His changeup was very good," agreed Power. "He threw 11 of them, and I think six of them were for strikes. He didn't only throw it when he was ahead, either. He threw it early in the count a couple of times."
After issuing another leadoff walk in the second, Chapman got Brian Horwitz to bounce into a double play. Major League veteran Brian Bixler opened the third with a double, the only hit allowed by the left-hander, who fell behind Trevor Crowe, 3-0, before striking him out. That started a run of six straight batters retired by Chapman.
The streak ended when Horwitz drew a leadoff walk in the fifth, but Chapman retired Chris Gimenez on a fly ball to right and Bixler on a forceout, then picked Bixler off first.
Chapman (0-1), who threw 87 pitches, did not return for the sixth inning.
"I worked with my off-speed stuff really well today," he said. "I mixed up my changeup and fastball. A lot of fans came to see me pitch today. I feel proud about that."
Clippers starter Yohan Pino (2-0) responded well to the pressure of squaring off against the highly touted southpaw. He gave up four hits and a walk over seven shutout innings, striking out six.
Power indicated working faster will be the priority for Chapman's next start.
"His tempo is very slow. He's starting to understand when he works faster, it helps the umpire call strikes and it helps his fielders behind him," he said. "He has picked up the pace a little, but you'd like to have the pitcher ready before the batter. That wasn't always the case [Saturday]."