WASHINGTON — Though he struggled briefly, closer Sean Doolittle made sure the Washington Nationals had something to show for a long day and night against the New York Mets.

Doolittle allowed a run before improving to 13-for-13 in save opportunities with Washington and the Nationals took advantage of four straight walks by Mets pitchers to beat New York 5-4 Sunday night, salvaging a doubleheader split.

Amed Rosario hit a solo homer in the eighth inning to lift New York to a 6-5 win in the first game.

"After a tough loss in the first game, a tough stretch of travel, we'll take it," Doolittle said. "This team has got a lot of character, a lot of fight. You saw that in both games today. That's why it was really huge for us to be able to seal that one up."

Doolittle gave up an RBI single to Jose Reyes with two outs in the ninth, but then got Juan Lagares to line out to left to stay perfect in save chances since a mid-July trade from Oakland. Doolittle was brought in to stabilize Washington's problematic bullpen and has a 3.00 ERA in 18 appearances with the NL East leaders.

"The only pitch I thought I missed and I want back is the one to Reyes," Doolittle said.

Tanner Roark pitched six innings of three-run ball and Adam Lind had a homer and two RBIs for Washington in the nightcap. Anthony Rendon and Wilmer Difo each added two hits, and Washington took advantage of four straight walks — three by reliever Hansel Robles (7-5) — in the sixth inning to force a split of the four-game series.

With a runner on first and New York leading 3-2, Robles walked three straight hitters to force in Difo. Chasen Bradford then came on and walked Andrew Stevenson, bringing Rendon home.

Robles also appeared in the first game and struck out the only batters he faced, Rendon and Ryan Zimmerman.

"He's better than that," Mets manager Terry Collins said. "We saw that in the first game today. He came in in a huge situation and struck out two of the best hitters in their lineup. You can't walk guys in the big leagues like that, three guys in a row."

Roark (11-8) allowed five hits and struck out nine without a walk.

"He picked us up big time, because if he goes out early we're in a real big mess," said reliever Shawn Kelley, who worked in both games.

Brandon Nimmo homered in the late game and added a single for the Mets. Reyes had three hits.

Lind's 11th homer of the season provided a vital insurance run in the eighth.

Mets starter Seth Lugo, who had been on the disabled list with a right shoulder impingement, was activated Sunday and allowed one hit through the first three innings in the nightcap.

After blowing a five-run lead in the first game, the Mets regained it and cut down the potential tying run at the plate for the final out.

Rosario fell behind in the count 0-2 against Joe Blanton (2-3) with two outs in the eighth before launching a shot to centre for the rookie's fourth home run.

With two outs in the ninth and pitcher Edwin Jackson pinch-running at first base, ex-Met Murphy sent a sharp grounder into right-centre field for a double. When rookie right fielder Travis Taijeron booted the ball, Jackson was waved around third.

Lagares, quickly backing up Taijeron, grabbed the ball and threw to second baseman Asdrubal Cabrera, who relayed a strike to catcher Travis d'Arnaud in time to get Jackson as he made a headfirst slide into home.

Cabrera's three-run homer in the first and Wilmer Flores' two-run shot in the third (his career-high 17th) staked New York to an early 5-0 lead.

Jerry Blevins (6-0) got the win and A.J. Ramos worked two innings for his 25th save in 27 chances.

HARVEY IS CLOSE

Mets RHP Matt Harvey (shoulder) tossed 4 2/3 innings in a rehab start Saturday for Double-A Binghamton, allowing five runs (three earned) and five hits. He struck out two and walked one. "Yeah, we're hoping his next one is a start with us," Collins said.

STILL WAITING

New York hasn't swept a doubleheader from the Washington/Montreal franchise since July 27, 1999 at Shea Stadium.

TRAINER'S ROOM

Mets: RHP Noah Syndergaard (torn lat muscle) is expected to throw batting practice again Wednesday in Florida.

Nationals: INF Adrian Sanchez was sent to the hospital for a CT scan Saturday night after being hit in the chest with a pitch while attempting to bunt. A team spokeswoman said Sanchez checked out fine, was kept overnight to monitor his breathing, and discharged.

UP NEXT

Mets: RHP Chris Flexen (3-2, 5.79 ERA) starts when the Mets open a three-game series Tuesday in Cincinnati.

Nationals: RHP Max Scherzer (12-5, 2.25 ERA) returns from the disabled list (neck inflammation) as the Nationals host the Marlins Monday in the first of three games.

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