WASHINGTON - Washington Nationals starting pitcher Stephen Strasburg said it was back tightness that forced him to leave after pitching just four innings on Sunday.

But four relievers, two pinch-hitters and left fielder Jayson Werth more than picked up the slack for Washington, which is trying to desperately to stay alive in the National League East division race.

Leadoff man Werth had a homer, double, walk and three RBIs, and the Nationals, despite another abbreviated start by Strasburg, battled back to beat the Miami Marlins 7-4.

"I tried to battle through it. It is something hard to explain," said Strasburg, who failed to pitch five innings for the sixth time this year. "The offense picked me up. The offense came through today."

The Nationals (66-63) won their fourth series in a row but remained 5 1/2 games back of the first-place New York Mets, who beat Boston 5-4.

"You could see the fight in the dugout," said Doug Fister, who got the win out of the bullpen. "Guys were making great plays" on defense.

The bench came through for Washington as former starter Fister went two scoreless innings and pinch-hitter Clint Robinson hit a two-run homer. For good measure the other pinch-hitter, Matt den Dekker, doubled in the eighth but was stranded.

"I am going to continue to be ready when my name is called," said Robinson, a 30-year-old rookie who hit his seventh homer of the year.

Miami (52-79) jumped out to a 3-0 lead on a homer by first baseman Justin Bour in the first but the bullpen couldn't hold up after starter Brad Hand (4-4) allowed five runs in 4 2/3 innings and fell to 0-6 against the Nationals.

"He just couldn't make some pitches there in tough situations when he needed to," Marlins manager Dan Jennings said.

The Marlins had three hits in the first inning against Strasburg.

"It was good to see us jump out the way we did," Jennings said. "So we gave Brad a little breathing room there and that's nice to have against this ball club that swings the bat like that."

Strasburg, who had back problems earlier this year, gave up seven hits and four runs in four innings while throwing just 60 pitches.

"He had some discomfort in his upper back," said manager Matt Williams. "The velocity came down a little bit today so we got him out of there. He had a little bit of discomfort in the last inning. We decided to get him out of the ballgame. You could tell with your eyes. We will give him some medication and see where he is in a couple of days."

But the offense saved the day as Robinson smashed a two-run homer in the seventh off reliever Erik Cordier to give the Nationals a 7-4 lead. It was his first career pinch-hit homer and fourth of the year for Washington.

The Nationals had taken a 5-4 advantage with three runs in the fifth. Werth had an RBI double and right fielder Bryce Harper and shortstop Ian Desmond, who walked a season-high three times, had RBI singles against Hand.

Marlins left fielder Derek Dietrich (two hits) led off the fourth against Strasburg with a solo homer -- his career-high 10th of the year -- to give his team a 4-2 edge. Strasburg hit 99 mph with his fastball in his previous start Tuesday at home against San Diego, but the fastball that Dietrich crushed was clocked at 93 on the stadium radar gun.

Werth's two-run homer in the third had pulled Washington to within 3-2.

"He is doing well in the leadoff spot," Williams said of Werth, who is hitting .325 with three homers in 10 games as the leadoff hitter.

Bour crushed a three-run homer to right off Strasburg to give the Marlins a 3-0 lead. It was the second homer of the series for Bour, a product of George Mason University in Fairfax, Va., and fourth of his 137-game career against his hometown club.

Strasburg had allowed just five runs in his previous four starts with 32 strikeouts and three walks in 26 innings.

Felipe Rivero, Drew Storen and Jonathan Papelbon each pitched a scoreless inning for the Nationals.

Papelbon recorded his 22nd straight save this year and fifth with the Nationals as he retired second baseman Dee Gordon on a grounder for the final out with two runners on base.

Center fielder Michael A. Taylor and third baseman Anthony Rendon also had two hits for Washington. Shortstop Adeiny Hechavarria had three hits for the Marlins, who had won six of the previous 11 games against Washington.

"A good offensive day," Williams said of the 13 hits, including five for extra bases.

NOTES: Washington LHP Gio Gonzalez (9-7, 4.11 ERA) will start Monday at St. Louis against Cardinals RHP John Lackey (11-8, 2.92 ERA). ... The Marlins begin a series Monday at Atlanta as LHP Chris Narveson (1-1, 7.04 ERA) will start for Miami against RHP Mike Foltynewicz (4-6, 5.71 ERA). ... Washington 1B Ryan Zimmerman entered Sunday with RBIs in six games in a row, and five of his previous six hits were for extra bases, including three homers. He was 1-for-4 with a single and no RBIs on Sunday ... Marlins 3B Martin Prado had a walk on Sunday and has reached base in 25 of his last 26 games. He entered Sunday hitting .333 against Washington this year, with an average of .364 at Nationals Park. He was 0-for-3 plus the walk on Sunday.