Harang (16-4) allowed two runs on six hits with six strikeouts and two walks for the Reds.
Brandon Phillips had two hits, two runs scored and an RBI in the win.
Jacque Jones drove in both Chicago runs.
Carlos Zambrano (16-13) was the losing pitcher after giving up four runs on seven hits over 5 1/3 innings..
The Cubs, who lost for only the second time in their last eight games, are tied with Milwaukee for the NL Central lead.