WASHINGTON -- New York Mets skipper Terry Collins managed the Sunday doubleheader as if they were the sixth and seventh games of the World Series.

Washington Nationals manager Dusty Baker fielded lineups in the two games that looked more like those from Grapefruit League action in early March.

After a day of baseball that lasted about 10 hours from the first pitch to the last -- with a break of 2 hours, 59 minutes between games -- the last two National League East champions split a pair at Nationals Park.

Tanner Roark, the Washington starter in the Sunday night game, gave up three runs on five hits in six innings as the Nationals won 5-4. He finished with no walks and nine strikeouts.

"I was keeping them uncomfortable up there," Roark said. "Confidence is a heck of a thing. The bullpen tonight was unbelievable."

In the first game, the Mets' Amed Rosario hit his fourth homer in his 26th major league game to break an eighth-inning tie for a 6-5 New York win. Rosario never hit more than three homers in a minor league season and had 10 career minor league homers in 1,382 at-bats before this year.

"I was just hoping to swing at a good pitch. I was just looking for the right pitch, and I guess I got it," Rosario said through an interpreter.

Jerry Blevins (6-0) got the win in the first game, and Joe Blanton (2-3) took the loss. AJ Ramos tossed two scoreless innings for his 25th save.

The Nationals were able to earn a split of the twin-bill as Roark had something the Mets didn't: control of the strike zone. The winning rally for Washington featured two Mets relievers walking four batters in a row.

"Tanner was great," said Washington reliever Shawn Kelley, who pitched in both games. "We needed that. He was able to get deep into the game. He picked us up big time."

Roark is 3-1 with a 3.48 ERA since the All-Star break, striking out 27 in five starts.

"We wanted a sweep," Baker said. "We had plenty of opportunity (in Game 1). You have to be satisfied with a split. It was a long three days since we got back from Houston."

Blanton came on to get the last out of the eighth in the second game. Closer Sean Doolittle pitched the ninth to pick up his 13th save with the Nationals since coming to the team in a trade with the Oakland A's in July.

Doolittle allowed an RBI single to Jose Reyes (three hits) before getting Juan Lagares for the final out on a liner to left.

The Nationals moved on top in the sixth inning of the second game when Mets pitchers lost the plate.

Michael A. Taylor and Andrew Stevenson both walked with the bases loaded to bring in runs, with the walk by reliever Chasen Bradford to Stevenson giving Washington a 4-3 lead. Hansel Robles (7-5) walked three batters in a row before Bradford took over.

"He is better than that. We saw that in the first game today," Collins said of Robles. "You can't walk guys in the big leagues. He has been so good lately. He just doesn't do that too much. We will have to talk to him about it."

Adam Lind gave Washington an insurance run with a solo homer off Erik Goeddel in the eighth to make it 5-3. It was Lind's 11th homer of the year.

Washington led 2-0 in the nightcap before Lagares doubled home Reyes in the sixth. Later in the inning, the 100th pitch of the night for Roark was sent over the fence in center by Brandon Nimmo, who gave the Mets a 3-2 lead with his two-run shot.

Roark (11-8) is now 7-2 in his career against the Mets as a starter and has not given up more than three runs in his last five outings.

Roark has walked just three batters in his past three outings combined. The Mets walked more than that in one inning Sunday night.

The first-place Nationals (78-51) improved to 11-5 this year against the Mets (57-73). Lagares and Nimmo had two hits apiece for New York in the second game, while Wilmer Difo and Rendon each had two hits for the Nationals.

NOTES: Washington RHP Erick Fedde was added as the 26th man for the doubleheader in order to start the first game. Nationals RHP A.J. Cole was sent to Triple-A Syracuse and OF Rafael Bautista was called back from Syracuse. ... The Mets activated RHP Seth Lugo from the disabled list and sent RHP Robert Gsellman to Triple-A Las Vegas. RHP Kevin McGowan was added as the 26th man for the doubleheader. ... Washington RHP Max Scherzer (12-5, 2.25 ERA) is slated to face Miami Marlins RHP Jose Urena (12-5, 3.68) on Monday at Nationals Park. ... Mets rookie RHP Chris Flexen (3-2, 5.79) will start Tuesday in Cincinnati against Reds RHP Sal Romano (3-5, 4.96).