Miley (5-7) logged his first victory in more than a month, taming the Rockies on five hits. He issued just one walk and struck out five, tossing 64-of-101 pitches for strikes.
His three-run double in second inning broke a scoreless tie and sent the National League West-leading D-backs on their way to a fourth straight victory.
Paul Goldschmidt and Martin Prado each added a two-run shot for Arizona.
Colorado's Drew Pomeranz (0-2) was lit up for five runs on five hits, lasting just four innings.
Carlos Gonzalez, named to the NL's All-Star Game starting lineup Saturday, went 4-for-4 with a solo homer for the Rockies.