The Rockies broke a scoreless tie in the seventh when Chris Nelson drew a leadoff walk from Dale Thayer (0-1).
After Yorvit Torrealba sacrificed Nelson to second, Helton came to bat for De La Rosa and golfed a 2-1 pitch over the right field wall for two runs.
De La Rosa (1-1) scattered two hits and four walks over six scoreless frames, while fanning four.
Jedd Gyorko supplied the only RBI for San Diego.
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