After Carlos Villanueva (2-4) set the Mariners down 1-2-3 in the 10th, Nate Schierholtz opened the 11th with a leadoff single off Oliver Perez (2-2) and Soriano followed by smashing a long homer to center field, finishing with three RBI.
Blake Parker tossed a 1-2-3 bottom of the 11th for his first career save as the Cubs rebounded from a 5-4 loss in Friday's series opener.
Starlin Castro also went deep for Chicago.
Justin Smoak cracked a solo homer in the Mariners' defeat.
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