Edinson Volquez (13-4) allowed one earned run and six hits, but the Astros chased him in the seventh inning with four unearned runs after two errors by shortstop Jeff Keppinger. Volquez struck out five batters as the Reds ended a five-game losing streak overall.
Dunn, who attended high school at New Caney north of Houston, recorded his second multihomer game of the month and Edwin Encarnacion added a solo shot for the Reds, who beat Houston for just the fourth time in the last 17 meetings.
The Reds beat the Astros for the first time since a 4-3 victory at Minute Maid Park on May 30, 2007.
Griffey’s homer was the 608th of his career, moving him within one of Sammy Sosa for fifth all-time. Griffey has 1,139 extra-base hits, one behind Ty Cobb for 10th all-time.
Rodriguez (6-4) lost for the first time in four starts. He lasted only 4 2/3 innings after allowing one run and striking out seven in each of his previous two outings.
Dunn sent his first solo homer into the upper deck in right in the second. Encarnacion then singled and scored on Joey Votto’s double to make it 2-0.
Volquez gave up a single to Kaz Matsui and a walk to Lance Berkman in the first, then retired the next eight batters. Berkman doubled to left with one out in the fourth, but Volquez struck out Carlos Lee and Geoff Blum.
Volquez and Jay Bruce singled to begin the fifth. One out later, Griffey launched Rodriguez’s 0-1 pitch into the upper deck in right, his 15th homer. Dunn then hit a two-run homer to center. Dunn has 32 homers - 12 this month and six since the All-Star break.
Rodriguez gave up six runs on nine hits, both season highs.
Hunter Pence led off the Houston fifth with a solo homer to left, his 14th.
Pence started Houston’s late rally with a double to right. Keppinger committed errors on consecutive grounders, allowing Pence to score. Ty Wigginton then hit a three-run homer to left.
