Stephen Strasburg was already enjoying one of the best pitching performances of his career when he added another memorable moment: A go-ahead home run.

Strasburg tossed a complete game six-hitter in addition to his fifth-inning shot, Wilmer Difo added a home run and the Washington Nationals defeated the Miami Marlins 4-0 on Wednesday to complete a three-game sweep.

"He was determined from the beginning," Washington manager Dusty Baker said. "You could tell by the look on his face. He had a great day. It was his day today. He hit, he pitched."

Washington, which has won four in a row, extended its lead in the NL East to 15 games over the Marlins.

The Marlins had no answer for Strasburg (11-4), who struck out eight. Strasburg threw 110 pitches. It was Strasburg's second complete game in 179 starts and his first since Aug. 11, 2013, against Philadelphia.

Strasburg is 1-1 with a 0.86 ERA in three starts since returning from a disabled list stint for right elbow nerve impingement.

"We were pretty much overmatched today," Miami manager Don Mattingly said. "He had 73 through seven innings, so 10 pitches an inning, basically."

Miami left-hander Adam Conley (6-6) made it through the first four innings unscathed before Strasburg launched the first pitch of the fifth to right-center for his second home run this season and third of his career.

"We haven't had BP in such a long time I really didn't have high expectations for not having picked up a bat ... since my start in San Diego (on Aug. 19)," Strasburg said. "I don't know. Sometimes you're just lucky."

Two batters later, Difo connected for his fifth homer of the year.

The Nationals outscored Miami 23-5 during the series, and the Marlins were 1 for 22 with runners in scoring position over the three games.

"Nothing really went right for us as far as getting runs across," Mattingly said.

Miami's Giancarlo Stanton, who leads the majors with 51 home runs and has 18 this month, went 0 for 4.

Anthony Rendon had a two-out RBI double in the seventh and Alejandro De Aza scored on a passed ball in the eighth to pad Washington's lead.

J.T. Realmuto had three hits for the Marlins, who went 2-8 at Nationals Park this season. Miami, which had won 13 of 16 prior to arriving in Washington, had not dropped three in a row since July 14-16.

"I think we just keep going," Conley said. "Three games at their place against the team leading our division doesn't outweigh how long we've been playing good baseball. We had to climb back quite a ways from however many months ago when people were writing us off. It's just three games."