"It was good to see him put a good swing on Harang after he missed a couple of days," Astros manager Cecil Cooper said.
Hunter Spence also homered in the fourth off Harang, who gave up three hits and three runs -- two earned -- in five innings.
Brandon Backe, competing for a spot in Houston's rotation behind Roy Oswalt, started and pitched four scoreless innings, allowing one hit. The Reds managed only three hits through the first eight innings and went to the bottom of the ninth trailing 4-0.
"He doesn't want us to take it easy on him," Cooper said. "I like that. If this was the regular season, he would have gone six innings."
Mike DeJean couldn't hold on against a lineup of minor leaguers finishing off the game. The 37-year-old reliever, in camp on a minor league deal, gave up a triple to Jose Castro and three consecutive walks. Kevin Barker followed with a run-scoring single, ending DeJean's outing.
Alvin Colina's three-run double off Ryan Houston won it.
"DeJean was uncomfortable out there," Cooper said. "He was sliding all over the place."
Reds manager Dusty Baker enjoyed the way his minor leaguers pulled it out after the regulars left the game.
"It's a beautiful thing," Baker said. "That's how I do things. If they come over from the minor league camp, they're going to play so we can see what they can do. That was sweet."
Notes: Astros RHP Chris Sampson was scheduled to pitch, but was scratched with a stiff neck. ... Reds LHP Bill Bray is scheduled to throw again Wednesday. He has yet to pitch in a spring game because of a sore left shoulder. ... Baker said utility player Jerry Gill is making "slow" progress in healing from a strained left thigh.