The Astros' No. 17 prospect allowed an unearned run on five hits and struck out nine over eight innings as Lancaster beat Modesto, 3-1.
The effort came days after the 21-year-old right-hander was promoted from Class A Lexington. He said he was aware of how hard it's supposed to be to pitch in the Cal League but didn't dwell on that as he prepared for his debut.
"My pitching coach in Lexington [Dave Borkowski] kind of told me about it," he said. "It's all a mental type of deal. I knew going in if I just keep attacking hitters, get ground balls, I'd be giving my team an opportunity to win my first game."
Tropeano joined the JetHawks after dicing up the South Atlantic League over the first half of the season, going 6-4 with a 2.78 ERA in 15 games, including 14 starts. Over 87 1/3 innings, he struck out 97 and walked 26.
Sunday marked the fourth time this season he'd struck out at least nine batters.
"I felt good out there, had my good stuff today," said the New York native. "I was just trying to work the fastball on both sides of the plate, get two strikes, get to an advantageous count."
Tropeano said he hadn't been expecting a promotion but obviously enjoyed getting the opportunity to climb to a higher level.
"It took me a little by surprise because we were coming on the last game of an eight-game road trip and they told me right before that I'd be going to Lancaster," he said. "I feel pretty settled in [so far]. There's a great group of guys here and they welcomed me with open arms."
Tropeano is in his second season since being selected in the fifth round of last year's Draft out of Stony Brook University. He said he was "real proud" of his alma mater for its recent run in the College World Series.
In his debut season, Tropeano was 3-2 in 12 starts for short-season Tri-City in the New York-Penn League. He posted a 2.36 ERA over 53 1/3 innings, striking out 63 and walking 21.
After Sunday's stellar introduction to the next level, he said he's looking forward to seeing if he can continue to tame the hitter-friendly Cal League.
"I'm real excited, real happy the Astros gave me this opportunity," he said.
Backing Tropeano up on Sunday were Domingo Santana, who hit a two-run homer in the first inning, and Astros No. 3 prospect George Springer, who added his 16th of the season in the ninth.