Two of the four runs in the sixth came on a throwing error by Bryce Harper, who left the game with a mild left hamstring strain.
Rays right-hander Chris Archer ended up with his eighth victory, pitching five innings and allowing three runs.
The Nationals are now a game over .500 (34-33), but are still a game and a half behind the first-place Mets, who lost to the Blue Jays. The Rays improved their record to 38-30 and remain in first place in the American League East.
"I think taking three of four from anybody is big," Rays manager Kevin Cash said after the game. "This team, they've got a lot of good players, they've got good pitching. We were fortunate to come out of here with three wins."
Fister is back: In his first game in over a month, Doug Fister lasted 5 1/3 innings and allowed five runs on eight hits. He was cruising until the sixth inning, when he allowed four runs.
"I felt a lot better. It's a work in progress," Fister said. "I know I keep saying that, but that's what it is. I got back some of my base and my roots. I have to get back to what I do best, and that is go with contact. You really have to build up to it. Any time you change mechanics or change your approach, you really do have to take a little bit of time and rebuild back up to midseason strengths."
The Nationals strike first: Washington took a 2-0 lead against Archer in the first inning. Harper highlighted the scoring with an RBI single. The team would then take a 3-1 lead in the second inning on an RBI single by Yunel Escobar.
"I got a little too slider-happy in the first inning," Archer said. "They were good starters but way off the plate, almost non-competitive pitches. The only ball that was hit hard was [a ground ball by] Harper"
Harper exits with injury: Harper had to leave the game in the sixth inning with a mild strain of his left hamstring. With the Nationals up, 3-2, Asdrubal Cabrera singled to right field and Harper tried to throw out Logan Forsythe at the plate, but Harper threw the ball into the Rays' dugout, allowing Steven Souza Jr. to score and Cabrera to take third base. After making the throw, Harper stayed on the ground for several minutes before he was taken out of the game and replaced by Clint Robinson.
"I put all the pressure on the left knee," Harper said. "I got my lower hamstring in the knee a little bit. It didn't feel very good. I was in pretty good pain. I was scared at the same time. I could feel a little more on the lower half of it. We'll see how I am with it tomorrow and we'll go from there." More >
"He can hit": When Rays manager Kevin Cash was asked before the game about Joey Butler earning the start in left field, his answer was simple: "He can hit, so he better hit." Butler proved Cash's words to be true, smacking several balls hard, but none farther than his solo home run in the sixth inning. The shot that kept on carrying and landed in the Nationals' bullpen was Butler's fifth home run of the season.
"It was a low-scoring game, at that point anyway," Butler said. "So any run was a good one. We were fortunate enough that happened with no outs and the team was able to build on it." More >
Rebound performance: Archer did not have his best stuff at the beginning of the game, but battled and improved to 8-4 on the season. Archer had already thrown more than 50 pitches after getting through two innings, and by then, the Nationals had already scored three runs. After that, the Nationals had little success. They managed three hits off Archer in his final three innings and no runners reached third base. He struck out three and walked two in his return to the mound where he made his Major League debut in 2012. More >
UPON FURTHER REVIEW In the first inning, Denard Span was called out on a stolen base attempt. Span thought he was safe on the play. Manager Matt Williams challenged the call and after 2 minutes and 26 seconds, the call was overturned and Span would later score on a single by Harper.
In the bottom of the second inning, Michael Taylor bunted back to Archer. Archer fielded and threw to first, bringing Jake Elmore into the basepath. Elmore lost possession of the ball and Taylor was ruled safe, but Cash challenged that Elmore made the catch before dropping the ball. After just over two minutes, the ruling was confirmed. Taylor was safe at first with a single.
RAIN DELAY For the second straight night, inclement weather forced the Nationals and Rays into a rain delay. Thursday night's was a brief 17-minute interruption in middle of the fourth inning and both starters remained in the game.
WHAT'S NEXT Rays: Tampa Bay's two-city road trip wraps up with a three-game weekend set in Cleveland on Friday at 7:10 p.m. ET. The Rays will throw Nate Karns (3-3, 3.67 ERA) in the opener.
Nationals: The Nationals will play a three-game series against the Pirates at Nationals Park starting Friday night at 7:05 p.m. ET. Right-hander Joe Ross will make his third straight start against an NL Central team.