The Marlins completed a three-game sweep of the Nats and finished May with a 21-8 mark, posting their most wins in any month in club history.
"Thanks to this month, we're in great position," said manager Ozzie Guillen after his team moved to within a half-game of the Nationals. "I don't look at months and days, I just look at the day we're playing the game. I don't see any reason why we will not continue to play the way we're playing. Overall, we played pretty well.
"We're going to be up and down. We're going to try to be up as much as we can. That's the coaching staff's job. That's my job."
Like the team, Stanton had a record-setting month. His 12 home runs matched Dan Uggla for the most by a Marlin in any month. Uggla did it in May 2008.
Stanton's 30 RBIs in the month match Miguel Cabrera (2006) for the most in May. The 22-year-old has made a strong case to be National League Player of the Month. He hit .343 (37-for-108) in the month.
"Things are finally coming together as they should," Stanton said of the Marlins' impressive run, which included going 7-3 on the homestand. "Long overdue. It seems these games we can finally show how good we are."
The more times Stanton blasts 400-foot home runs, the more notoriety he will receive. The right fielder is ready for the attention.
"I feel like the expectations have been there, regardless," said Stanton, who emerged as a force as a 20-year-old rookie in 2010. "Being more popular or whatever comes with the territory. It's better to be good and popular than someone who is like, 'He's an OK player.'"
Stanton's home run off Ryan Perry in the seventh provided an insurance run.
"You can't make a mistake on a hitter that's big and strong like him, and boy, Perry threw a little backup slider and he straightened it out," Nationals manager Davey Johnson said.
In all three games of the sweep, Heath Bell collected the save. The right-hander stranded runners on first and third by striking out pinch-hitter Rick Ankiel for his 10th save of the season.
Bell preserved the win for Johnson, who improved to 8-0 with a 3.24 ERA in his career against the Nationals.
"It's what we expected coming into Spring Training," Johnson said. "With all the guys we brought over, and guys maturing, we can win a lot of games, and it's starting to show."
Johnson wasn't at his best, but he found a way to minimize seven hits over six innings. His velocity picked up, reaching 96 mph.
A year ago, Johnson missed most of the season due to right shoulder inflammation. He threw 60 1/3 innings total in 2011.
On Wednesday night, his six innings give him 63 1/3 on the season.
"Physically, I feel great," Johnson said. "I'm still having some ups and downs. But I'm a little more comfortable each time out. It seems like consistency still isn't there, but it is coming."
The Marlins took a 4-3 lead for Johnson in the fifth on John Buck's infield RBI single. Hanley Ramirez doubled to get the inning going. Stanton was hit by a pitch on his left forearm and Nationals starter Chien-Ming Wang was replaced by Ross Detwiler.
With one out, Bryan Petersen walked to load the bases. Buck bounced a grounder into the hole at short. Ryan Zimmerman made a diving stop, and his throw from the ground pulled second baseman Danny Espinosa off second base. It was initially ruled an error, but changed to an RBI single.
It was an uphill climb for the Marlins, who fell behind by two in the fourth.
Washington's Adam LaRoche doubled to open the fourth, and he scored on Espinosa's one-out RBI single. Roger Bernadina ripped an RBI double, but on the play, he was thrown out trying to stretch the hit into a triple.
On the slide, Ramirez was shaken up as Bernadina's right foot slid into the third baseman's right foot. For a few seconds, Ramirez was on the ground in pain, but he was able to walk it off.
Capitalizing on two walks by Wang to open the fourth inning, the Marlins pulled even at 3. Logan Morrison and Petersen each walked and advanced on a groundout. Chris Coghlan lifted a sacrifice fly to left, and Johnson came through with a two-out, broken-bat RBI single. Jose Reyes singled in the inning, extending his hitting streak to 11 games.
In the first inning, the Marlins went ahead on Omar Infante's double and Stanton's two-out single to left.
Stanton drove in 15 runs in the 10-game homestand.
"It was a good team month," Johnson said. "Everybody was chipping in, doing their part: Stealing bases, running the bases well, tagging up ... little things we do. Whatever it takes, we're doing it."