"I don't think I've managed a game in 11 years where nine home runs were hit," Rockies manager Jim Tracy said.
Joey Votto, Jay Bruce, Brandon Phillips and Todd Frazier homered for the Reds, while Troy Tulowitzki, Carlos Gonzalez (twice), Michael Cuddyer and Dexter Fowler homered for the Rockies.
Eight of the homers -- including all five by the Rockies -- were solo shots. Phillips hit a three-run homer in the third to give the Reds a 5-1 lead. Cuddyer's homer, estimated at 448 feet, was the longest of the day.
The Rockies' five homers out-distanced the Reds' four homers 1,917 feet to 1,591 feet -- more than 3,500 total feet in all.
Starters Jamie Moyer and Mat Latos allowed all nine home runs. It is the most home runs allowed by Moyer since he allowed five to the Red Sox on July 21, 2006.
Location was an issue for Moyer, who said he missed his spots against Bruce and Phillips, but added that the pitch to Votto may not have been a strike.
Gonzalez collected his third multi-homer game of the season, and has 10 round-trippers overall.
There were 29 home runs hit on the Reds' homestand -- a Great American Ball Park record for a homestand of seven games or fewer.