Pittsburgh padded its lead in the eighth inning, when infielder Chris Bostick and catcher Jin-De Jhang ripped back-to-back home runs to right field.
The Pirates struck first, as McCutchen doubled and came home on Polanco's single off Gabriel Ynoa in the first inning. Ynoa retired all three hitters he faced in the second.
"In the first inning, I was going too quick towards home plate," Ynoa said through a translator. "In the second inning, I was more calm, under control."
The Orioles tied it up in the fourth on Anthony Santander's RBI single off Pirates setup man Daniel Hudson, driving in Adam Jones, who doubled.