The game had been deadlocked since the fourth inning, during which Helton's two-run single allowed the Rockies to overcome a 6-4 deficit.
With Arizona's Bryan Shaw on the mound for his first inning of work in the eighth, Carlos Gonzalez reached on a single to left. Gonzalez moved to third on an errant pickoff attempt by Shaw (0-1), after which Helton doubled to left.
That run gave the win to Rex Brothers (1-1), who allowed a hit in the top of the eighth. Rafael Betancourt gave up a one-out single but nothing more in the ninth for his second save.
Arizona suffered only its second loss of the season, wasting early offense that included a two-run homer by Miguel Montero during a four-run third.