HOUSTON -- If Johnny Cueto wasn't feeling well Saturday night it was certainly difficult to tell.
Jordan Smith pitched a perfect ninth to complete the shutout.
Cueto has been on antibiotics for a sore throat, but said his illness didn't affect his play.
"I am always thinking about positive stuff," Cueto said in Spanish through an interpreter. "I know that I have to go out there every time and just try to do a good job for the team and pitch good."
Reds manager Dusty Baker said the illness may not have been a bad thing for Cueto.
"He was actually more relaxed out there," Baker said. "I have seen that a number of times. A guy is a little underneath the weather, so he relaxes. They don't have any choice, and they don't overthrow."
The win moves the Reds ahead of St. Louis atop the NL Central standings after the Cardinals dropped their third straight on Saturday.
Votto hit a two-run home run in the first inning and Hernandez, who also drove in a run in the third, added a solo shot in the second.
Houston starter Roy Oswalt (6-12), who has requested a trade, had one of his worst outings of the season. He allowed nine hits and six runs in five innings.
"It was so out of character because he's thrown the ball so well," Astros manager Brad Mills said. "There was no reason to think that he wasn't going to come out and be the same guy that he has been. It was very surprising."
Oswalt was looking for his 144th career victory, which would have tied him with Joe Niekro for first place on the team's all-time win list. Instead he took another loss, which could be his last as an Astro with the July 31st trade deadline approaching.
Oswalt said the pressure of the trade deadline and trying to match the record didn't bother him on the mound.
"No," he said. "I've thrown enough starts not to worry about one."
Cueto (10-2), who struck out six, didn't allow a hit until a double by Angel Sanchez with no outs in the fourth inning. But he retired the next three batters to end the inning. He allowed a single in the fifth before pitching a perfect sixth inning.
Chris Johnson singled in the eighth inning before reaching second on an error when Orlando Cabrera missed the catch which allowed Jason Castro to reach first. He pitched out of that jam by retiring the next three Astros, striking out one.
"I went out there today just concentrating on my location more," Cueto said. "I wanted to make sure I did not go out there and over throw. I just feel better and better every time I go out there."
Votto's two-run shot to the Crawford Boxes in left field put Cincinnati up 2-0 in the first inning. It was his second straight game with a homer and his 25th this season.
The Reds pushed their lead to 3-0 when Hernandez led off the second inning with his homer.
Cabrera and Votto hit consecutive doubles in the third inning before they both scored on a double by Laynce Nix. Hernandez drove in Nix with a single to right field that made it 6-0, but Hernandez was tagged out at second for the third out.
After the game, Houston optioned Sampson to Triple-A Round Rock and recalled LHP Fernando Abad from Double-A Corpus Christi. ... The Astros wore the rainbow-sleeved, button up white uniforms that were worn by the team from 1989-93 on Saturday night. ... Houston RHP Brian Moehler, who has a strained right groin, isn't ready to come off the disabled list. The Astros aren't sure when he'll be healthy enough to pitch again. "He's still feeling a little tightness," manager Mills said. "There's not a lot of pain there but when he tries to extend and finish his pitches then there's a grab and there's a pull. We want him to be 100 percent before he gets back out there." ... Gary Matthews Jr., who was playing for Triple-A Louisville, opted out of his deal after the Reds didn't bring him up to the majors on Saturday. Baker said he spoke to Matthews on Saturday morning and tried to persuade him to stay with the team for a while, but Matthews said he simply didn't want to be in Triple-A any longer. ... RHP Homer Bailey (inflamed right shoulder) is scheduled to make a rehabilitation start on Monday for Single-A Dayton.