Nationals starter Jordan Zimmermann outdueled Jake Arrieta over six innings and left with a 1-0 lead. The Cubs tied it in the seventh on Starlin Castro's sacrifice fly against Drew Storen.
Denard Span's hustle turned a soft hit to right field off Pedro Strop (1-4) into a double leading off the eighth. Two outs later, the Cubs intentionally walked Adam LaRoche to bring up Zimmerman, who ripped a single to left that scored Span.
Tyler Clippard (6-2) pitched the eighth inning, and Rafael Soriano earned his 21st save for the Nationals, who have won seven of eight.
Washington took two of three games in the series, including 13-0 on Saturday to break Chicago's four-game winning streak.
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