The Cincinnati ace outpitched Clemens (2-4) and dominated the Astros for the third time this season, leading the Reds to a 2-0 victory.
Harang (11-6) gave up four hits and struck out six with one walk in eight innings. He held the Astros to five hits in victories April 29 (6-3) and June 2 (14-3).
"I'm feeling good overall," he said. "I'm executing my pitches, I'm able to hit my spots and I'm getting outs in key situations."
The Reds beat the Astros for the sixth time in seven games. The defending National League champions also fell six games behind Cincinnati in the wild-card race. Houston has mustered two runs or fewer in four of Clemens' seven starts. In his four losses, the Astros haven't scored a run before he has left the game.