Arroyo (16-10) tossed six innings of one-run, limiting the Astros to four hits and a walk while fanning five as the first-place Reds reduced their magic number for clinching the National League Central to eight.
Houston starter Nelson Figueroa (5-3) was touched for five runs (three earned) on seven hits in 4 1/3 innings.
The Astros were paced at the plate by Carlos Lee, who went 3-for-4 and hit his 23rd home run of the year.
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