Strasburg allowed one run on four hits and struck out four batters. His only blemish came in the sixth inning. Jordany Valdespin led off with a single, and he scored when Giancarlo Stanton swung at a 2-1 curveball and hit it down the left-field line for a double. Strasburg was trying to throw the ball down and away, but he left it up in the zone.
Stanton, who ended up going 2-for-3 with two RBIs, has given the Nationals problems even since he entered the league in 2010. In 63 games against Washington, Stanton is hitting .313 with 21 home runs and 50 RBIs.
After Stanton drove in his second run of the game in the eighth inning off reliever Aaron Barrett, Williams said there wasn't a thought about walking Stanton intentionally.
"I think Aaron got ahead of him with two strikes and hung a breaking ball, so whether it's Giamcarlo or anybody else, if he makes the proper pitch, he gets him out," Williams said. "He swung at two sliders in a row, and he threw the other one for a strike and let him hit it."
Asked why Stanton continues to torture the Nationals, Strasburg said, "He is a good mistake hitter. I just got to do a better job executing pitches."
Strasburg's outing was a vast improvement from his previous outing against the Rockies, in which he allowed four runs in 5 1/3 innings.
"I was trying to keep the ball down and pitch to contact -- trying to go in and out," Strasburg said.
The Nationals had right-hander Henderson Alvarez on the ropes twice during the game. In the second inning, Washington had the bases loaded with no outs, but Danny Espinosa struck out, Marlins third baseman Casey McGehee made a diving catch on a liner off the bat of Nate McLouth and Strasburg grounded out to end the threat.
"That's baseball. I think [Alvarez] will be the first to tell you that he wasn't on top of his game early," Strasburg said. "He seemed to pitch when it mattered. He erased all the balls he was leaving over the plate."
Before the game, Alvarez said he didn't feel right while throwing in the bullpen, but he managed to get his act together.
"I was in the bullpen and I didn't feel like I always feel before I hit the field. I wasn't into it. For several innings I had to fight through it," Alvarez said. "When the bases loaded with nobody out, I started to find my control of my pitches and of the game."
In the sixth, Anthony Rendon led off with a double, but he was left stranded at second base.
Alvarez (8-5) pitched seven shutout innings, and he allowed three hits and struck out four batters.
In the ninth inning, the Nationals made it interesting against Marlins closer Steve Cishek. They had the bases loaded with two outs, but Rendon struck out to end the game. Washington finished 1-for-11 with runners in scoring position.
"Those guys are excited. There's a lot of confidence in there," Marlins manager Mike Redmond said of his team. "They're having fun. We're relaxed. We feel like we're in the game no matter what happens -- even if we go a few innings without scoring or getting a hit. There's a lot of confidence in there right now."
Despite the loss, the Nats retained their half-game National League East lead over the Braves, who also lost Tuesday night at Dodger Stadium.