It was the first time this season that the veteran slugger has hit more than one round-tripper in the same contest.
Soriano hit the first pitch by Pittsburgh starter Tom Gorzelanny (3-4) in the bottom of the first inning into the left-field stands and launched a three-run blast in the second.
Aramis Ramirez had one RBI while Soto and DeRosa also had two hits for the NL Central Division-leading Cubs, who have won eight of their last 10 home games against Pittsburgh and rose to 7-0 in the season series.
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