Reynolds (8-3) notched his first triumph since July 2, 2011, when he was a member of the Rockies, holding his former team to three runs on seven hits. The right-hander didn't issue a walk and struck out five as the Reds evened their three-game series.
Shin-Soo Choo went 3-for-4 with a run-scoring double for Cincinnati, which remained 3 1/2 games out of first in the National League Central.
Rockies starter Juan Nicasio (8-7) took the loss, surrendering six runs on seven hits over 4 1/3 innings.
Corey Dickerson smacked a two-run homer for Colorado.
Caroline Berg Eriksen: Soccer player's wife triggers debate with post-birth selfie
Theater accidentally screens 'Nymphomaniac' trailer instead of Disney's 'Frozen'