WASHINGTON -- Stephen Strasburg had just pitched a gem, but his manager already was looking to the future.

"We just have to see how he comes out of this one," Washington Nationals manager Dusty Baker said after Strasburg threw a six-hit shutout to defeat the Miami Marlins 4-0 on Wednesday.

The cause for concern goes back to the famous shutdown of Strasburg in 2012. And as recently as his previous start Thursday at Houston, Strasburg left the game after six innings with cramps.

Strasburg looked the part of the overall No. 1 draft pick on Wednesday, as he tossed 110 pitches for his first shutout since Aug. 11, 2013, against the Philadelphia Phillies. It was the second shutout and complete game of his career.

"Sometimes it is just your day," Baker said. "Boy that was some ballgame. It was his day today."

But the season is becoming pretty special as well for the Nationals and Strasburg, who lowered his ERA to 2.90 to rank fourth in the league and also hit his third career homer and second this year.

"I take it one inning at a time," said Strasburg, who wasn't thinking about a complete game early on. "The game is way too hard. I was trying to take it one pitch at a time and go as long as I can."

"(Jose Lobaton) called a really good game. I tried to add a couple of pitches, throw a couple of pitches early that produce quick outs and not be so heavy on the fastball. I was just trying to hit my spots."

To show how confident Strasburg is with his changeup, he threw one with a 2-0 count to Derek Dietrich with a runner on third and no outs in the fifth. Dietrich fouled it off and eventually struck out swinging and Strasburg got out of the inning after a leadoff triple to J.T. Realmuto.

Wilmer Difo (2-for-4) also homered as the Nationals swept the three-game series.

"It is great. He has done so well," Difo said of Strasburg. "You want to make the plays for him."

The Marlins entered the day 5 1/2 games back of the Colorado Rockies for the second wild-card spot in the National League. The first-place Nationals (81-51) have won four in a row while the Marlins (66-66) were outscored 23-5 in the series.

Strasburg (11-4) had eight strikeouts and one walk. He hit his second homer of the year when he lined the first pitch from Marlins starter Adam Conley in the last of the fifth into the seats in right-center. The ball was hit 100 mph by Strasburg.

Two batters later, Difo lined a solo homer to left to give the Nationals a 2-0 lead off Conley. It was the fifth homer of the year for Difo, who started at second after playing right field for the first time Tuesday night.

Anthony Rendon (2-for-4), a Houston native who has family effected by Hurricane Harvey, had an RBI double in the seventh with two outs for a 3-0 cushion. His hit off Drew Steckenrider scored Trea Turner, who walked and stole his 36th base a day after coming off the disabled list.

The Nationals added a run in the eighth on a passed ball to make it 4-0.

Strasburg has not allowed a run in his last 15 innings.

"Pretty much overmatched," Marlins manager Don Mattingly said of Strasburg. "He had 73 pitches through seven innings. Ten pitches per inning basically."

Conley (6-6), who gave up 11 hits and five runs at Washington on Aug. 9, allowed two runs in six innings Wednesday. Realmuto (3-for-3) also had a single and double, and Dee Gordon had two hits.

"J.T. lead off with a triple. We left him there," Mattingly said of the key fifth.

But the day belonged to Strasburg. "We have not had BP in so long. I didn't have a lot of expectations," he said of his homer.

Marlins slugger Giancarlo Stanton, who has 51 homers, was 0-for-4 against Strasburg.

"It's a great challenge," Strasburg said. "There are probably going to be a lot more challenges down the road. He is a true professional."

NOTES: Washington RF Bryce Harper (hyperextended left knee) told reporters before the game he is "a long ways from running" and has no idea when he will return. He was injured running to first in a home game Aug. 12 against San Francisco. ... The Nationals begin a series Thursday in Milwaukee and LHP Gio Gonzalez (13-5, 2.40 ERA) will face RHP Zach Davies (15-7, 3.91) of the Brewers. ... The Marlins begin a series at home Thursday, and RHP Odrisamer Despaigne (0-1, 3.70) will make his third start of the year against Phillies RHP Ben Lively (1-5, 3.46). ... Marlins manager Don Mattingly said Wednesday he hopes injured 1B Justin Bour (right oblique strain) can play in some minor league rehab games this weekend. Most minor leagues end regular-season play Monday. "We are running out of time," Mattingly said. Bour, who has 21 homers, has been on the disabled list since July 25.