The first half of the season didn't go as expected for the Miami Marlins. The second half didn't get off to a good start.

The division-leading Washington Nationals stretched their lead over the Marlins to 10 games with a 5-1 win Friday night that was powered by a two-run home run by Ryan Zimmerman.

"I'm not going to panic yet," Marlins catcher John Buck said.

The Marlins have lost three straight.

"Why wouldn't we be optimistic?'" Buck said. "We've got a good club. We haven't played well. We've underachieved. Do we make it hard on ourselves? Yes, but we've got a good enough team that with the addition of Carlos (Lee) we have enough to close the gap."

Jesus Flores drove in two runs for the Nationals, who have won six of eight.

Nationals starter Jordan Zimmermann (6-6) pitched six scoreless innings allowing four hits and striking out six as he lowered his ERA to 2.48. He is one of two pitchers in the majors who has pitched at least six innings in each of his starts this season.

"Last year I thought he pitched like a No. 1 (starter) and he's continued this year," Nationals manager Davey Johnson said. "He's been not getting hardly any run support, but he's growing up even more this year."

Josh Johnson (5-6) lost to Washington for the first time in his career as he allowed five runs and 11 hits in 5 1-3 innings. Johnson was 8-0 in 15 starts against the Nationals.

"Pretty bad, not the way you want to start the second half," Johnson said.

The Marlins were out-hit 13-7 and have dropped three straight.

"We couldn't put it together," Marlins manager Ozzie Guillen said. "Zimmermann threw the ball pretty good. Today, we took it like another All-Star break day. Hopefully tomorrow we can come back and swing the bats better."

Ian Desmond's RBI single scored the Nationals' first run before Zimmerman connected off Johnson to left-center field in the third to make it 3-0.

"He's always good," Zimmerman said of Johnson. "He's not a fun guy to face, but he made a mistake and I put a good swing on it."

Zimmermann allowed three hits to the first five batters before settling down. He was at his best in the fourth inning when he struck out Logan Morrison, Hanley Ramirez and Justin Ruggiano, all swinging.

"I had a pretty good fastball tonight and I was able to locate it pretty well," Zimmermann said. "I was just spotting up with that and I got some swings and misses."

Adam LaRoche singled to lead off the sixth, his third hit of the game, and Desmond followed with a hit. Flores drove them both home with a single to left that dropped right in front of Morrison. LaRoche crossed home plate just before Desmond, who was only three steps behind and extended the lead to 5-0.

"Desi is a lot faster than Adam," Zimmerman said. "I guess Adam was going to tag up and score if the guy caught it with his speed. It was one of those funny plays. I'm just glad they both scored."

Flores' hit ended Johnson's outing.

The Marlins threatened in the seventh when Zimmermann left in favor of Henry Rodriguez. After Buck's RBI single scored Ruggiano to make it 5-1, Austin Kearns lined into an inning-ending double play to pitcher Michael Gonzalez, who relieved had Rodriguez.

Ruggiano stole a career-high three bases.

NOTES: Zimmerman's home run was his 15th against the Marlins, the most he's hit against any club. ... Ramirez was dropped to fifth in the lineup for the first time in his career after closing the first half on a 2-for-22 slump. "Hanley is struggling at the plate," Guillen said. "As Hanley starts hitting better he will be moved back to where he is supposed to be (in the third spot)." ... Miami placed OF Giancarlo Stanton (right knee surgery) on the 15-day DL, retroactive to July 8, and activated OF Emilio Bonifacio (left thumb surgery) off the 15-day DL after Bonifacio missed 46 games. Stanton is expected to miss 4-6 weeks. "I don't know (when I'll be back), I just started walking," Stanton said. "I honestly have no idea. They say four to six weeks, but I've got no clue." ... Marlins first-round pick LHP Andrew Heaney signed a $2.6 million bonus just before Friday's deadline and was in attendance. ... Miami-native LHP Gio Gonzalez (12-3, 2.92 ERA) will start Saturday for the Nationals against LHP Mark Buehrle (8-8, 3.25 ERA), who has won his last three starts.