CINCINNATI -- The Houston Astros were well on their way to a doubleheader sweep when a costly error wrecked those plans.
Houston scored four times in the first inning of the nightcap, but the Reds' offense and a fielding miscue turned the game around.
A throwing error by Astros starter Ezequiel Astacio, recalled earlier Saturday, led to four unearned runs. That helped the Reds rebound from a 4-3 loss in the opener of the doubleheader, forced by a rainout Thursday night.
"I'm not happy at all," Houston manager Phil Garner said. "We had the game. We make a play and we're probably out of that inning with no runs."
Adam Everett homered for the second time in two games and the Astros rallied three times for the Game 1 victory.
Ramon Ortiz, pitching on fewer than four days rest for the first time in his career, allowed four runs and five hits in the first inning of the nightcap. He recovered and retired 15 straight batters, allowing the Reds' offense to stage a comeback.
"I didn't change anything," Ortiz said. "They hit everything. I said, 'There's nothing I can do about it. Just keep pitching.'
"If we win every time, I'll pitch on two days rest."
Ortiz (4-6) allowed six runs, five earned, and eight hits in 6 2/3 innings. He lasted only two-plus innings in an 11-3 loss in St. Louis on Wednesday.
"In the first inning, his breaking ball was flat," manager Jerry Narron said. "He made an adjustment and gave us a great outing. He gave us a chance to win the ballgame."
Astacio (0-4) gave up seven runs, three earned, and 11 hits with one walk and six strikeouts.
His fifth-inning error changed the game.
With the Reds trailing 4-3, Lopez led off the inning with a triple. One out later, Ken Griffey Jr. hit a comebacker to Astacio, who threw wildly to first base. Lopez scored and Griffey was awarded second base when Astacio's throw bounced into the stands.
"I tried to make a perfect throw, and I threw it too easy," Astacio said. "I tried to forget about it and make better pitches."
"He was in control," Garner said. "He can't let something like that bother him."
Griffey scored to give the Reds a 5-4 lead when Wily Mo Pena doubled up the left-center field gap. Jacob Cruz followed with a run-scoring single, snapping a career-worst 0-for-16 slump, and he scored on Javier Valentin's double off the left-field wall.
Jose Vizcaino and Lance Berkman had run-scoring singles in the seventh to cut Cincinnati's lead to 7-6.
The Reds scored four times in the eighth inning on a two-run homer by Griffey, an RBI single by Lopez and a sacrifice fly by Ray Olmedo.
Orlando Palmeiro led off the game with a home run, his second homer of the season and the second leadoff shot allowed by the Reds this season. The Astros increased their lead to 4-0 on Chris Burke's two-run double, a passed ball and Brad Ausmus' squeeze bunt.
Lopez started the Reds' first with his 14th homer and Cincinnati's first leadoff home run since Dunn hit one against Philadelphia on June 14, 2003. Dunn cut Houston's lead to 4-3 with his 21st home run, a two-run shot in the third.
In the opener, Houston rookie starter Wandy Rodriguez (4-3) recorded back-to-back wins for the first time in his career. The right-hander allowed three runs, five hits and five walks while tying his career best with six strikeouts in six innings.
Mike Burns pitched two scoreless innings of relief, and Dan Wheeler pitched the ninth for his second save in three tries this season. He also got the save on Friday while closer Brad Lidge remains day to day with a slight elbow problem.
Reds starter Aaron Harang (4-7) fell to 0-5 in his last six starts. The right-hander, who recorded his last win by beating Roger Clemens and the Astros 9-0 in Houston on May 30, allowed eight hits and four runs in seven innings.
Lopez finished 4-for-5 with two RBI and three runs scored in the nightcap. ... To make room for Astacio on the roster, Houston designated 44-year-old reliever John Franco for assignment. ... Craig Biggio's first-game double was his 2,721st career hit, tying him with Lou Gehrig for 51st on the career list. Roberto Alomar is 50th with 2,724. ... Willy Taveras' bunt single in the first game was his 16th of the season, tying the Astros' record set by Steve Finley in 1991. ... Morgan Ensberg got hits in both games to extend his hitting streak to a career-high nine. ... Reds 1B Sean Casey celebrated his 31st birthday.