Fowler's slam came in the eighth inning, capping a 13-hit attack, and Tyler Colvin had a solo homer and three RBI for the Rockies, who evened a three-game series.
Chacin (2-4) limited the Padres to one run on five hits, yielding two walks and striking out four.
Padres starter Edinson Volquez (9-10) was roughed up for five runs on nine hits in a 4 2/3-inning effort.
Will Venable clouted a solo homer for San Diego.
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