That brought up Rosario, who smacked a 1-0 into the left-center field gap, sending both runners home for an early lead the Rockies wouldn't relinquish.
Colorado added two more runs in the sixth on a throwing error by Volquez and a Dickerson sacrifice fly en route to a victory in the first of a three-game set.
Tyler Chatwood (5-2) went 6 2/3 innings to notch the decision, yielding two runs on five hits. He allowed three runs and struck out four.
Volquez (6-7) was tagged for four runs on eight hits over 5 1/3 frames as the Padres remained winless in July.
Everth Cabrera and Kyle Blanks each drove in a run for San Diego.
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