"Just a good gesture. I hope Nick saw it. He knows we miss him," catcher Brian Schneider said.
Armas pitched six strong innings for his first victory in seven starts since Aug. 18 and Ryan Zimmerman hit an RBI double for Washington, which sent the NL East champions to their seventh defeat in 10 games.
"Was that like, win one for the Gipper?" Nationals manager Frank Robinson said. "That just kind of got the guys up a little bit."
Trying to secure a spot in New York's postseason rotation, Steve Trachsel (15-8) allowed three runs in five-plus innings. He dropped to 1-3 with a 4.91 ERA in his last four starts -- not exactly what the Mets were looking for heading into October.
"Tryouts are for spring training. If 15 wins is not enough, then I don't know," Trachsel said.
The Mets have lost four of five to Florida and Washington.
Armas (9-12) gave up five hits, including Jose Valentin's 18th homer. He walked none and struck out four, earning only his third win since coming off the disabled list on July 17. He had been out with a strained right forearm.
Armas was 0-4 in his previous six starts since beating Philadelphia 6-4.
"I just want to be able to go out there every five days and be healthy," he said. "I know I can do my job."
One day after Johnson was hurt in a gruesome collision with right fielder Austin Kearns, the Nationals got a nice all-around game from Soriano, the first player in major league history with 40 homers, 40 steals and 40 doubles in one season.
"That's been what he's done all year long for us. He doesn't have to always hit a home run to help this ballclub," Robinson said. "His overall game, he brings a lot to the table."
Soriano hit a sacrifice fly in the first, doubled and scored in the fifth, and threw out a runner on the bases from left field.
Cliff Floyd tried to stretch a single in the fourth, but Soriano cut him down out at second for his major league-leading 22nd outfield assist.
"I enjoy every part of the game," Soriano said. "That's why I love this game."
Trachsel pitched 6 1/3 shutout innings in the division clincher Monday night against Florida. This time, however, he walked his first batter, Bernie Castro, who scored on Soriano's sacrifice fly.
Another walk helped the Nationals load the bases with none out in the second, and a run scored on Armas' double-play grounder.
Valentin connected leading off the fifth, a shot into the right-field bullpen.
Soriano opened the sixth with a double that glanced off the glove of third baseman Chris Woodward. Zimmerman followed with his second double of the day, making it 3-1 and chasing Trachsel, who yielded eight hits and three walks while throwing 92 pitches.
"He got some work in," Mets manager Willie Randolph said. "I don't look at Steve Trachsel like he's auditioning for a spot. He's been one of our best pitchers this year. It's not like it's the first time he's been around the block. When he gets runners on base, he knows how to handle that."
Brandon Harper doubled leading off the seventh against Darren Oliver and scored on a double by pinch-hitter Henry Mateo that appeared to bounce foul down the first-base line. First base umpire Tim McClelland initially signaled foul, then reversed his call.
Mateo scored on an RBI single by Felipe Lopez for a 5-1 cushion.
- Mets CF Carlos Beltran missed his sixth straight game with a strained quadriceps but is expected to play Monday night.
- New York SS Jose Reyes stole two bases, giving him 60 this season and matching his NL-leading total from last year.
- The Nationals improved to 5-9 against the Mets this season.
- RHP Philip Humber made his major league debut for the Mets and pitched a hitless ninth with one strikeout.