Matt Wieters hit a tiebreaking grand slam off Carl Edwards Jr. in Washington's five-run eighth inning, helping the Nationals beat the Chicago Cubs 9-4 on Sunday.
Bryce Harper started the winning rally with a one-out infield single against Mike Montgomery. Ryan Zimmerman doubled against Edwards and Daniel Murphy was walked intentionally to load the bases.
Washington then grabbed control in a span of two pitches. Edwards (3-3) hit Anthony Rendon, tying it at 4, and Wieters followed with a drive over the wall in center for his third career grand slam.
Wieters drove in five runs and Brian Goodwin homered for the NL East-leading Nationals, who had dropped three of four.
Willson Contreras homered twice for NL Central-leading Chicago. The Cubs closed out a 2-4 homestand against contenders Arizona and Washington before pulling on leather vests and bandannas for their "Easy Rider"-themed six-game road trip out west.
Brandon Kintzler (3-2) pitched a scoreless inning for his first win since he was acquired in a trade with Minnesota.