Brett Myers pitched seven scoreless innings, Humberto Quintero drove in two runs and the Astros held off a late rally to slow the Reds' drive for their first NL Central title since 1995 with a 4-3 victory.
They begin a three-game series with the Brewers on Monday before a trip to San Diego.
"It still hurts today but we gotta move on to Milwaukee and play them tougher than we played today," Reds manager Dusty Baker said.
Rookie Chris Johnson had a solo home run in the seventh inning to help the Astros to the win. With St. Louis' 4-1 win over San Diego, Cincinnati's magic number for winning the division title remained eight.
Myers (13-7) extended his streak of consecutive starts of six or more innings to begin a season to 31. It is the longest such streak since Curt Schilling did it in his first 35 starts in 2002. Myers yielded six hits and struck out five for his fifth straight win.
He is 8-0 with a 2.01 ERA in 14 starts at home this season.
"I'll reflect on it at the end of the year," Myers said of his success this season. "I'm just going to go out there and keep pitching and just follow the plan. I've just got to keep working and keep going at it hard."
The Reds trailed 4-0 in the eighth inning before Jay Bruce followed Joey Votto's second double of the game with an RBI single.
"We had more opportunities than they had," Baker said. "We outhit them tonight. We just made some mistakes on location, missed the cutoff man, and made some more mistakes on location and it ends up costing us. It was a tough game to lose."
Lyon said Houston is playing with confidence.
"I don't think there's any doubt in this locker room of how well we can play," he said. "We're playing good right now no matter who we play."
Reds starter Travis Wood (5-4) allowed four hits and three runs with five strikeouts in six innings.
Jason Michaels was hit by a pitch in the fifth inning before a double by Johnson that rolled into the right field corner. Then with one out, Quintero drove in two runs with a single to make it 2-0. He advanced to third base on an error by Hernandez.
Quintero scored on a sacrifice fly by Myers to push the lead to 3-0.
"I felt pretty good up there," Wood said. "But in that fifth inning, they got a couple of timely hits, starting with me hitting Michaels in the forearm and then they put a couple of hits together and scored a couple of runs."
Votto doubled with two outs in the third inning but Myers retired the next nine batters. Jonny Gomes got Cincinnati's next hit with his with two outs in the sixth. Bruce walked after that, but the Reds came up empty when Hernandez grounded out.
The Reds got a pair of singles in the first inning, but Myers retired Bruce for the third out.
Wood didn't allow a hit until Michael Bourn's single with no outs in the fourth inning.
- Bourn left late in Sunday's game with a mild right oblique strain and is listed as day to day. Bourn said he expects to miss a couple of days with the injury.
- Rolen was not in the lineup Sunday, but pinch hit in the ninth inning. Reds manager Dusty Baker said he's just a little "banged up."
- Baker said he isn't sure if RHP Homer Bailey will make his scheduled start at Milwaukee on Monday. He left his last start after experiencing dizziness in the fifth inning. Baker said he had to consult with the team trainer before he makes the decision.
- Houston RHP Bud Norris will make his scheduled start on Monday despite the injury to his left shin. Norris was hit by a line drive on the first pitch of his last start but remained in the game. He has a large bruise on his shin and had his leg wrapped in tape from the knee to the ankle on Sunday, but said he's OK.