Pittsburgh starter Erik Bedard left the game after one inning due to back spasms and the Pirates sent five more pitchers to the mound to hold down the Nationals.
McCutchen had an RBI single during a three-run third and scored the final run of the inning on an infield base hit by Casey McGehee. McCutchen added a solo homer in the eighth.
Brad Lincoln (2-0) replaced Bedard in the second and got the win with a three-inning effort that included just one hit and four strikeouts.
Washington lost its third in a row and has dropped six straight road outings. The setback went to Ross Detwiler (3-2), who allowed three runs on seven hits in six innings.