WASHINGTON -- The Florida Marlins keep putting pressure on the teams ahead of them in the NL wild-card race.
"Yeah, that's what you've got to do. You've got to keep trying to win ballgames. I'm glad we've got four in a row and hopefully [we] keep going," manager Fredi Gonzalez said.
Pinch-hitter Brett Hayes also homered for the Marlins and Johnson (14-4) allowed two hits over five innings. The right-hander walked three, struck out one and retired his final 11 batters in Florida's fourth straight victory. He is 7-2 in his last 10 starts, and 5-0 in his career against the Nationals.
"I finally found a groove and was throwing my slider for strikes. It was a good slider," Johnson said. "Some little things mechanically were a little bit off in the first two innings, but after that it was good."
Washington's losing streak is its longest since the team dropped 12 straight from Aug. 8-20, 2008. The Nationals are 10 defeats shy of their second straight 100-loss season.
"It stinks," outfielder Josh Willingham said. "Have we lost 90? It's hard to believe. ... We just haven't put it together as a team very often."
Florida took advantage of Livan Hernandez's wildness to build a 3-0 lead in the first. Cameron Maybin and Ramirez drew one-out walks before an RBI double by Cantu. After John Baker struck out, Dan Uggla walked to load the bases and Ross followed with a two-run single.
Johnson's brief control problems allowed the Nationals to get to 3-1 in the second. Washington loaded the bases on Adam Dunn's single and two walks before Pete Orr punched an RBI single to right -- the last hit the Nationals got until the sixth.
"If we get a little more that inning, it changes the complexion of the game a little," Nationals interim manager Jim Riggleman said.
Maybin's sacrifice fly and Ramirez's two-run homer, his 20th, made it 6-1 in the fourth.
Hernandez (7-10) was pulled after allowing six runs and eight hits over five innings. He walked four and struck out six.
Johnson was removed after five innings and 82 pitches because Gonzalez was worried that throwing 48 pitches in the first two innings might have overextended him.
"I know they're going to be watching out for me a little bit, so those are just those things that you can't do anything about," said Johnson, who wanted to stay in the game.
Said Gonzalez: "Obviously, you want him to go deeper in ballgames so you don't have to keep taxing your bullpen, but we've got to [take] first things first. J.J. is a big part of us for a long time."
Hayes, batting for Johnson, led off the sixth with his first career homer, a shot to left on an 0-2 pitch from Victor Garate, who was making his major league debut. It was Florida's fifth pinch-hit homer this season.
Later in the inning, Cantu's RBI double made it 8-1.
Ramirez doubled home a run in the eighth.
Pinch-hitter Mike Morse drove in a ninth-inning run with a double for Washington.
Ramirez's next home run will be the 100th of his career. ... Coghlan's leadoff single in the first extended his hitting streak to a career-high 13 games. That matches the longest by a rookie this season -- Pittsburgh's Andrew McCutchen from June 11-25. ... Washington 3B Ryan Zimmerman grounded into his team-high 19th double play to end the first. ... Cantu's 28 first-inning RBIs are tops in the majors.