Bryce Harper's two-run homer in the bottom of the 13th inning lifted Washington past the Mets 5-3 Thursday and gave the Nationals a season-high 4 1/2-game lead in the NL East.
The Nationals take that margin over the reeling second-place Braves into a three-game series that opens Friday at Atlanta. The Braves were off Thursday after an 0-8 road trip against the Dodgers, Padres and Mariners.
Harper's shot to left on a 1-0 pitch off righty Carlos Torres (5-5) after Ian Desmond's leadoff walk was only the fourth homer of an injury-plagued season for the 2012 NL Rookie of the Year.
It was the second game-winning homer of Harper's career. The other came July 25, 2013, against Pittsburgh.
His latest big hit also came a day after a little stir created by a radio talk-show host's question to manager Matt Williams about whether it might make sense to send Harper to the minors to help him get out of a slump that had him hitting .250 entering Thursday.
The teams used a total of 15 pitchers, eight by New York.
Washington's Craig Stammen (2-4) gave up one hit in three innings for the win.
Washington won despite blowing a 3-1 lead. Desmond had a homer and three RBIs, and Jordan Zimmermann allowed one run through his first six innings. But the righty departed with two men on and one out in the seventh, and reliever Drew Storen proceeded to let both inherited runners score.
The Mets tied it at 3 thanks to a wild pitch, a sacrifice fly by Eric Young Jr., and an RBI single by Curtis Granderson.
Once Storen was lifted for lefty Jerry Blevins, Washington's bullpen retired 15 consecutive batters.
Mets rookie Jacob deGrom's five-start winning streak ended. He gave up three runs in six innings.
The temperature was 80 degrees for the unusual 12:35 p.m. start on "Camp Day," with hundreds of kids in the upper deck cheering raucously at even the most routine out recorded by Washington's fielders and rhythmically chanting "Strike him out!" or "Let's go, Nats!" They had cleared out by the time extra innings arrived.
After the first of Adam LaRoche's two doubles on the day, Desmond drove a full-count fastball into the visiting bullpen beyond left field for his 18th homer and a 2-0 lead in the second.
That ended deGrom's franchise rookie record for consecutive innings without allowing a homer at 67 1-3.
Desmond added an RBI single in the fourth, when left fielder Young made a casual throw, allowing LaRoche score despite a bad jump from second.