"It was exciting and everybody is pretty pumped up," said Dominguez, who took a shaving cream pie to the face after the game. "Everybody knows how good [Chapman] is. I just happened to put a bat on it and it just happened to go out of the park. Good win for us."
The one-out rally was started by Tyler Greene, who hit a soft liner to right field. Pinch hitter J.D. Martinez blooped a single between three Reds in left field to put two on and bring Dominguez to the plate.
Dominguez faced a tall challenge, as Chapman entered the game with a 0.30 ERA against National League hitters, holding them to a .113 average.
But the 23-year-old connected for the second homer of his career and the Astros' 19th come-from-behind win of the season.
"That's a good team over there. It felt like Rocky against Apollo Creed today," DeFrancesco said. "When Chapman was in there, we watched him last time dominate the game and today, we got to him. I'm real pleased with the way they competed."
Except adding to the drama in this movie, Rocky was also nursing an injured wrist.
Dominguez was left out of the lineup for the second time Friday because of his wrist, but was called upon in the third inning when Jose Altuve left the game with a lower left abdominal strain.
DeFrancesco previously said Dominguez might have been available later in the contest if batting practice went well, but had to turn to him earlier than expected when Altuve went down.
"Today, I could still feel it, but with all the adrenaline and stuff going during the game, you don't really feel it too much," Dominguez said of his wrist. "It feels good."
It felt good enough to give the Astros the game-winner as well as field some crucial balls that ended up saving the game.
The Astros jumped out to an early 2-0 lead with a 2-run home run from Justin Maxwell in the first. The advantage didn't last long as the Reds fired back with two runs of their own in the bottom half of the frame off Astros starter Lucas Harrell.
Harrell allowed the first four Reds to reach base before eventually settling in to retire nine of the next 10 batters he faced. He ran into a one-out, bases-loaded jam in the fifth that had all the makings to ruin Houston's night.
But Harrell connected with Chris Snyder and Dominguez to turn a double play and get out of the inning with just one run crossing the plate. At the time, it gave up the Astros lead. In hindsight, that play saved the day.
"The defense played great behind me," Harrell said. "To not give up three or four right there is huge. If you can get out of that inning, you can start to build a little momentum off that even though you gave up a run."
Harrell said he didn't feel that he pitched well, giving up three runs on seven hits and walking four through six innings, but his efforts were enough to give the Astros their 43rd win of the year.
"They're playing us tough," said Reds outfielder Chris Heisey. "Maybe they're not motivated because they're not going to make the playoffs. But they're motivated because they're trying to get jobs for next year. So they're busting their butts and playing hard."
With all the growing pains Houston has experienced this season, DeFrancesco said it feels extra special to come out on top in game like this -- a feeling the Astros haven't felt too often recently.
"That was exciting," DeFrancesco said. "That was worth the whole time I've been here. I thought it was a well-played game. That's all we're asking for -- go out and compete, keep the mistakes at a minimum and give us a chance and that's what they did."