The Astros' right-hander remained perfect against the Reds, and Houston completed a three-game sweep with a 3-1 victory on Thursday night.
Oswalt improved to 15-0 in 19 appearances against Cincinnati, the most wins without a loss by any pitcher against one team in major-league history.
"I know eventually it's going to run out," he said. "I don't really think about it going into the game, but I know about it."
Lance Berkman homered for Houston. Oswalt (16-11) is 4-0 against the Reds this season.
"It's a combination of things," Astros catcher Brad Ausmus said. "When you have a record like that, it's got to be some luck. But he's also one of the best pitchers in the league and certainly that's a big part of it."
Oswalt went 5 2/3 innings and had a season-high 11 strikeouts.Ken Griffey Jr. singled and Adam Dunn walked with two outs in the sixth. Mike Gallo relieved and got Sean Casey to fly out to end the inning.
Oswalt, who allowed five hits and one walk, is 2-3 in his last seven starts.
"When he sees a Reds uniform, he has to feel pretty confident," Gallo said.
Brad Lidge pitched the ninth for his 32nd save in 35 opportunities, keeping the Astros a half-game behind Philadelphia in the NL wild-card race.
"It's certainly unusual," Houston manager Phil Garner said, referring to Oswalt's streak against the Reds. "But how do you figure something like that? He pitched a good game. He located the ball very well at the bottom of the zone and when you do that, you're going to have success."
The Reds were just as baffled.
"It's just amazing to watch him," manager Jerry Narron said. "He's got good stuff and his breaking ball really freezes guys. Tonight he had outstanding command and kept the ball down.
"He's one of the best pitchers in baseball. We couldn't get anything going even when he was out."
Casey got two hits off Oswalt but also is amazed.
"He definitely has our number," Casey said. "But he probably has a lot of teams' numbers.
"He's one of those special guys in the league with dominating stuff. It's the reason why Houston's back in the race."
Cincinnati won 14 of 16 road games before this series.
"This was a frustrating series for us. Their pitchers really shut us down," Casey said.
Aaron Harang (9-12) allowed three runs and five hits in seven innings.
"In a game like tonight, it all comes down to whoever makes the fewest mistakes," Harang said. "They got a couple of hits with men on base and that was it. You feel like you can't make any mistakes when Oswalt is throwing."
In the second, Dunn doubled and scored on Casey's single to the left-field corner. Casey was thrown out by Luke Scott trying to stretch the hit into a double.
Scott's RBI triple tied it in the fourth for Houston.
Willy Taveras singled to right-center to drive in Ausmus with the go-ahead run in the fifth, and Berkman hit his 14th homer in the sixth.
- Morgan Ensberg's 94 RBI are one short of tying the Houston record for a third baseman set by Sean Berry in 1996.
- Cincinnati is 1-8 in Houston this season.
- Casey's second-inning single gave him a 12-game hitting streak.
- Reds SS Felipe Lopez is 1-for-21 in the last five games.
- Houston's Jeff Bagwell had two singles, an RBI and a walk in his second rehab start at Corpus Christi.