Tony Sanchez socked a solo homer for the Pirates, who with their sixth win in seven games retained at least a share of first place with St. Louis in the National League Central.
Chicago's Pedro Strop (2-2) absorbed the loss.
Welington Castillo bashed a two-run homer as the Cubs fell for the fourth time in five games.
Toddler uninjured after being knocked over by Obama family dog
Exploding whale video goes viral on Internet