CHICAGO -- 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 Rendon also had an RBI double for the NL East-leading Nationals, who had dropped three of four.
Brian Goodwin homered, drove in two runs and robbed Jon Jay of a hit with a terrific diving catch on a sinking liner to center in the seventh.
Willson Contreras hit two more home runs for Chicago, which stayed a half-game ahead of second-place Milwaukee in the NL Central.
The Cubs closed out a 2-4 homestand against NL contenders Arizona and Washington before pulling on leather vests and bandannas for their "Easy Rider"-themed six-game road trip out west.
Cubs starter Jon Lester was charged with three runs and six hits in 6 2/3 innings.
Contreras led off the fourth with a drive to the back of the bleachers in left for his 20th homer. He connected again in the sixth, and Kyle Schwarber followed with another homer off rookie Erick Fedde for a 4-1 lead.
The 25-year-old Contreras is batting .346 (27 for 78) with 10 homers and 29 RBIs in 20 games since the All-Star break. He went deep five times in the last four games of the homestand.
But that was it for Chicago, which couldn't get anything going against Washington's bullpen after Erick Fedde lasted 5 1/3 innings in his second major league start. Brandon Kintzler (3-2) pitched a scoreless inning for his first win since he was acquired in a trade with Minnesota.
The Nationals faced the Cubs without their three best starting pitchers. Max Scherzer was pushed back after he left his previous start with neck spasms. Gio Gonzalez is on the paternity list, and Stephen Strasburg is on the 10-day disabled list with a right elbow injury.
Cubs outfielder Jason Heyward doubled in the eighth for his 1,000th career hit. He went 3 for 4.
The Cubs recalled infielder Tommy La Stella from Triple-A Iowa and optioned left-hander Rob Zastryzny to their top farm club. The 28-year-old La Stella is hitting .298 with two homers and six RBIs in 37 games with the Cubs this year.
Cubs: SS Addison Russell (strained right foot) thinks he will be able to return when he is eligible to come off the 10-day disabled list next Sunday. "It's something where I feel like I could try and play through, but really all it takes is just one kind of play to make it worse than what it already is," he said. "So taking the precautions and doing the treatment now."
Nationals: There has been no confirmation of Washington's rotation for its four-game series against Miami beginning on Monday night. Scherzer (12-5, 2.21 ERA) could start the opener against the Marlins.
Cubs: RHP Jake Arrieta (10-8, 3.88 ERA) faces Giants LHP Matt Moore on Monday night. Arrieta is 3-2 with a 2.08 ERA over his last six starts, showing flashes of the form that helped him win the NL Cy Young Award in 2015. Moore (3-11, 5.80 ERA) is trying for his first win since June 20.