Colorado scored nine times in the first three innings and was then held in check until Arenado greeted Joe Thatcher (2-1) with his fifth home run of the year.
San Diego tied it at 9-9 with a five-run seventh featuring a two-run homer by Carlos Quentin and a solo shot from Jedd Gyorko. Cameron Maybin singled in the fourth run of the inning and eventually scored on an infield single by Everth Cabrera.
Todd Helton had a two-run double during Colorado's three-run first and the Rockies then scored five times in the second to seemingly take control. Carlos Gonzalez had a two-run triple in the big inning and scored on Helton's base hit.
The teams combined for 33 hits. Matt Belisle (4-2), however, did not allow a hit while working the eighth and ninth innings to collect the victory.
2014: The Year in Music [PHOTOS]