It was the Reds’ largest winning margin and Houston’s ninth loss in the last 10 games.
In his sixth start, Arroyo (1-2) retired the first nine batters before walking Craig Biggio to start the fourth. Mike Lamb singled and Biggio scored on a sacrifice fly by Luke Scott later in the inning.
Arroyo walked Lance Berkman to start the sixth and retired the next six batters before being replaced by John Coutlangus in the eighth.
Arroyo allowed three hits and one run with five strikeouts.
The Reds also got help from Ken Griffey Jr., who was back in the lineup after missing three of the last four games because of a chest problem. He went 3-for-3, with a home run and two RBI, for his first three-hit game of the season.
In the third, Houston starter Matt Albers gave up back-to-back homers to Griffey and Alex Gonzalez. Griffey’s landed in the right field bleachers and the one by Gonzalez sailed to the Crawford Boxes in left field. Dunn reached first when Berkman couldn’t handle his grounder.
Dunn stole second base before scoring on a single by David Ross. Arroyo singled before an RBI-single by Josh Hamilton that made it 6-0 chased Albers.
The Reds got two runs in the second on an error by Lamb, the third baseman.
Albers (0-1) allowed eight hits and six runs - three earned - in 2 1/3 innings. He walked one and struck out two.
Brian Moehler allowed one hit and struck out two in 2 2/3 innings.
Scott Hatteberg doubled in the sixth off reliever Trever Miller and scored on a single by Griffey. Gonzalez followed with a double before Dunn’s three-run homer. It was Dunn’s seventh homer and made it 10-1, causing a chorus of boos and sending scores of fans streaming for the exits.
Biggio tripled in the eighth for his 2,954th hit and scored on a single by Berkman.
Carlos Lee then hit a grounder to Gonzalez who made an unassisted double play by tagging Lamb and stepping on second to put Berkman out.
