Florida has dropped four in a row and 10 of 12. Another loss, or a Houston victory, will knock the Marlins out of NL wild-card contention.
After the game, the Marlins announced they sent pitcher A.J. Burnett home for the remainder of the season. It came a day after Burnett, who can become a free agent after this season, complained that the coaching staff is too negative.
"In the best interest of the team, A.J. was advised to leave the team and he has done so," Marlins general manager Larry Beinfest said. "There will be no multiyear contract offer made to him."
Carrasco (5-3), a former reliever making his fourth start this season, allowed two hits, three walks and struck out six. He has not given up a run in his past three starts, spanning 17 2/3 innings.
"I'm surprising myself," Carrasco said. "I'm surprised at the way I've been pitching. This is the first time in my whole career that I'm pitching the way I'm pitching now."
Jason Vargas (5-5) was the tough-luck loser. He yielded one run and five hits in seven innings.
"You have to go out and play every day like it's your last game," said Vargas, 0-4 in his past seven starts. "You have to think of there being something still to play for, and that's what we're doing. Things just aren't going our way around here lately."
The victory snapped a three-game skid and gave Washington its second win in nine games. The Nationals moved above .500 again at 79-78.
"They see the finish line and they don't want the season to slip away," Nationals manager Frank Robinson said. "They want to finish above .500. They have pride."
Guzman, hitting .215 overall, is batting .338 (23-for-68) in his past 21 games.
"I want the season to start over right now, but it's almost over," he said.
Nationals right fielder Jose Guillen left after being hit by a pitch in the third inning. Guillen has a bruised left hand and is day to day.
- Beinfest said Burnett was not suspended and would be paid for the rest of the season.
- Marlins LF Miguel Cabrera was not in the lineup because he was serving a one-game suspension for violating a team rule.
- Florida's Mike Lowell was back at third base after starting the previous three games at second. Joe Dillon started at second.
- Robinson said right-hander Esteban Loaiza, originally listed as Washington's starter for Tuesday night, will go Wednesday instead. Tuesday's starter was to be determined, with a committee effort by the bullpen likely.