Hernandez (6-5) allowed two runs and five hits to end a four-game losing streak and earn his first win since he tossed seven scoreless innings June 7 at Washington. The right-hander improved to 3-0 with a 1.17 ERA against Washington this season and 8-1 with a 2.74 ERA against the Nationals in his career.
"You want to pitch different every time you play a team," Hernandez said. "What I do is try and throw some pitches they haven't seen before."
Hernandez pitched for the Nationals franchise for four seasons, its last two in Montreal and first two in Washington. He is 11-5 with a 3.67 ERA against the club for his career.
"I was kind of anxiously waiting for him to get through the first inning, and once he did that, he began to cruise," Mets manager Jerry Manuel said.
Hernandez got lots of help from Francoeur, who went deep for the first time since he was acquired from Atlanta on July 10. He finished with three hits and two RBI for the injury-riddled Mets.
"We've been pressing a little bit," Francoeur said. "I know it's been a little difficult time in here."
Francoeur had been shocked by the trade from his hometown team, and was unnerved by a quick return with New York last weekend.
"I'm not going to lie to you. I didn't know it was going to be so emotional in Atlanta," he said. "It was definitely a little difficult the first couple of games."
The Mets have scored six runs or more just six times in 25 games since All-Star center fielder Carlos Beltran went on the disabled list on June 22. They improved to 10-15 over that stretch.
Washington has lost six straight to lower its major league-worst record to 26-66 and is 0-5 since Jim Riggleman became interim manager a week ago.
The Mets pushed across two runs in the first and three in the second against J.D. Martin (0-1), who was making his major league debut. Daniel Murphy had an RBI single and Francoeur doubled in a run in the first. Angel Pagan and Luis Castillo had two-out RBI singles in the second, and Murphy followed with a run-scoring double.
Riggleman was impressed with Hernandez's effort.
"He's just the ultimate pro. He's a thinking man's pitcher," he said.
The 26-year-old Martin, who was recalled from Triple-A Syracuse on Sunday, allowed five runs and eight hits in four innings.
Francoeur led off the ninth with his sixth homer.
- New York general manager Omar Minaya said chief operating officer Jeff Wilpon recently gave him and Manuel a vote of confidence.
- The Mets placed RHP Fernando Nieve on the 15-day disabled list with a strained right thigh. He's expected to miss at least six weeks. Nieve suffered the injury running the bases in Sunday's loss in Atlanta. OF Cory Sullivan was recalled from Triple-A Buffalo.
- LHP Scott Olsen, who was placed on the 15-day disabled list with a back injury, saw Dr. James Andrews in Birmingham, Ala., and Riggleman said there was damage to his labrum.
- 3B Ryan Zimmerman was given the night off by Riggleman.
- OF Gary Sheffield (sore right hamstring) may be ready to pinch hit on Tuesday, but won't start, Manuel said.