Bryce Harper hit a two-run homer in the seventh inning and the Nationals rallied past the Cubs 6-5 to sweep a doubleheader delayed more than 3 1/2 hours by rain.
Max Scherzer pitched a complete game and Washington took advantage of the sloppy Cubs for a 10-3 victory in the opener. By the end of a long night, Chicago's lead in the NL Central was down to 2 1/2 games over Milwaukee.
Anthony Rendon's double off Steve Cishek scored Trea Turner to pull Washington to 5-4 in the seventh inning of the nightcap. Left-hander Justin Wilson (4-4) came on to face Harper, who drove a 1-1 pitch to straightaway center field for his 32nd home run. Harper also walked three times.
''Patience, really,'' Nationals manager Dave Martinez said when asked what it took to get through the very long day and night.
''It was nasty. It's nasty for both teams. We're pretty much at the mercy of the league and the rain, really. I'm proud of the guys just sticking in there and finishing the job.''
Rendon had a solo homer and Adrian Sanchez added two hits and two RBIs for Washington.
Wander Suero (2-0) got two outs for the win. Following an 89-minute rain delay in the middle of the eighth, Greg Holland worked the ninth to earn his second save in a game that ended at 1:44 a.m. on Sunday.
Victor Caratini hit his first career grand slam off Nationals starter Jefry Rodriguez to give Chicago a 4-0 lead in the fourth.
Washington pulled to 4-3 in the sixth on Rendon's homer and an RBI double by Sanchez.
Cubs starter Cole Hamels left with the lead after allowing three runs in 5 2/3 innings.
''We got on top, we had a nice lead, Cole was pitching well and all of sudden they just rallied from behind,'' manager Joe Maddon said. ''We had the right pitchers lined up, they were rested, and (the Nationals) got us. They absolutely got us.''
Bidding for a third straight NL Cy Young Award, Scherzer (17-6) gave up nine hits and struck out 11 without a walk. He also had an RBI single, raising his batting average to .270 this season.
It was one of just six hits for Washington, which capitalized on nine walks and three errors by the Cubs. The Nationals scored five runs in the sixth on just two hits thanks to two errors and a wild pitch that resulted in a run.
Martinez visited Scherzer on the mound after the Cubs scored twice in the ninth, but left his ace in to get the final two outs.
''He asked me what I wanted to do. I said I wanted to finish it,'' Scherzer said, noting the 66-degree game-time temperature had him feeling good. ''We've been playing some hot games and for the weather to cool off, you just felt like you had unlimited energy and for me, I still had plenty in the tank.''
Scherzer retired 15 in a row during one stretch. He lost his shutout in the seventh.
It was Scherzer's second complete game of the season and 10th of his career.
After Friday night's game was rained out following more than four hours of delays, the start of Saturday's first game was held up by showers for 2 hours, 10 minutes.
Maddon went with a bullpen game, and the Nationals jumped in front early. Jaime Garcia (3-7), making his Cubs debut, walked the bases loaded with one out in the first inning and Juan Soto sent a hard grounder past first baseman Anthony Rizzo that was ruled a two-run single. That was all for Garcia, and Washington's Matt Wieters provided a third run with an RBI single.
A LA CART
Sean Doolittle of Washington became the first reliever to use the Nationals Park bullpen cart, which debuted Aug. 17. ''I had a lot of fun,'' Doolittle said. ''It was a really smooth ride.''
The Nationals held a ceremony on the field between games placing outfielder Jayson Werth in their Ring of Honor. Signed to a $126 million, seven-year contract as a free agent after the 2010 season, Werth hit .263 with 109 homers and 393 RBIs and served as a team leader. The Nationals, who had not made the postseason prior to his arrival, won four NL East titles during his time with them. Werth threw out the ceremonial first pitch before the second game, with his son catching.
Cubs: RF Ben Zobrist returned for the opener after being out of Friday's lineup due to neck stiffness.
Cubs LHP Mike Montgomery (4-5, 3.76 ERA) opposes Nationals RHP Erick Fedde (1-3, 6.00) in Sunday's series finale.
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