"The arm felt really good -- nice and loose. I felt 100 percent. I didn't know [where the pitches] were going today," Strasburg said. "It happens being on the DL, coming back maybe expecting a little too much of myself. It kind of got to my head a little bit out there. I'm going to keep things simple next time."
The Marlins scored in the top of the first inning, as Dan Uggla belted a two-run homer over the left-field wall.
Strasburg had an easy second inning, but had a tough time getting Uggla out an inning later. Uggla took a 2-1 pitch and doubled to left field, scoring Hanley Ramirez and Gaby Sanchez.
"I missed the location completely," Strasburg said. "The fastball was away. He touched it. The next pitch to Uggla was the same story. I went out there and made a lot of mistakes. If I went out there and made one less mistake, it could have been a totally different ballgame."
Even Uggla and Ramirez, who had three doubles in the game, noticed a difference in Strasburg on Tuesday compared to his last start against the Marlins on July 16. In that game, Strasburg pitched six shutout innings.
"It's his first start back since a couple of weeks ago, when something was bothering him," Uggla said. "He was out there, kind of feeling for it. His command wasn't as good as the first time we faced him. His stuff was there, though. His fastball is explosive. His curveball had good break on it. The biggest difference was his command."
Said Ramirez, "Second time facing him, It's not the first time any more. When you haven't seen a guy, you don't know his command or his release point. We've seen it a couple of times now. We adjusted to it."
In the fifth, Strasburg allowed a leadoff double to Ramirez. Two batters later, Sanchez hit a line drive to left fielder Josh Willingham that should have been caught, but the ball tipped off his glove and dropped in for an RBI double.
Strasburg left the game after Sanchez's double and was replaced by right-hander Miguel Batista, who didn't fare any better. After facing three batters, the bases were loaded when Wes Helms drove in two more runs with a double. Strasburg was charged with one of those runs.
"Everybody is human. They are going to have these days sooner or later," Strasburg said. "I'm a little disappointed in myself, because I really went out there not focusing on the one thing that you really have to focus on: Just going out there and competing, and going with what you had. I spent the whole time worrying about trying to fix what was going wrong instead of just letting it go -- just throwing the ball."
Craig Stammen, making his first relief appearance as a member of the Nationals, allowed an RBI single to Logan Morrison in the sixth to make it a seven-run game.
Marlins right-hander Anibal Sanchez was the antithesis of Strasburg -- pitching 6 2/3 innings and allowing two unearned runs on five hits.
One run was scored in the second inning. With runners on first and second with two out, Ian Desmond hit a routine ground ball that went under the glove of Helms at third base, allowing Ivan Rodriguez to score.
In the seventh, the Marlins committed another error and it helped Washington score another run.
"He's actually putting together a very good year," Nationals manager Jim Riggleman said of Sanchez. "We don't know him, of course, the way we have seen Josh Johnson and Ricky Nolasco. We don't know as much about him, but the few times we've seen him, he's been very good.
"He was really good tonight. He reaches back and throws 93 [mph] when he wants to and pitches 88-90 at times changing speeds, cutting balls, good breaking ball. He had it all going."
The Nationals have lost three straight, dropping to 49-64.