Cuban-born veteran Livan Hernandez makes what could be both game series.
The 38-year-old Hernandez, who's made 473 consecutive appearances as a starter, will be shut down in that role for the rest of the season to allow Washington to make room for returning phenom Stephen Strasburg and other youngsters in the rotation.
Hernandez said he's willing to return next season as a long reliever with the Nationals, but not in any other cities.
"It's part of the game," he said. "I want to help the young guys. I don't know what's going to happen next year. I want to try to come back and be a long reliever only for this team. I will not do it for anybody else. Let's see the situation. I'll give it a chance. I explained how much I want (to be in Washington) to (general manager Mike) Rizzo. Let's see what happens."
Hernandez has allowed three runs or less in two of his last four starts in getting wins at Philadelphia and Atlanta. He allowed five hits and two runs in seven innings to the Braves on Aug. 30 while walking three and striking out one.
He's 13-15 in 39 career starts against the Mets with a 4.06 earned run average.
In Saturday's middle game, Ryan Zimmerman knocked in the decisive runs with a bases-loaded single in the bottom of the ninth inning to send the Nationals to an 8-7 win.
With the Nationals trailing, 7-6, Jesus Flores singled off Bobby Parnell (3-5) to begin the ninth-inning rally, and pinch-runner Brian Bixler moved to second on a wild pitch before Johnny Gomes walked and Ian Desmond laid down a sacrifice bunt.
With one out, the Mets rolled the dice by intentionally walking Roger Bernadina to load the bases for Zimmerman, who shattered his bat on an up-and- in fastball. The ball fell into shallow right field, giving the Nats the walk-off victory.
Sean Burnett (5-5) worked the top of the ninth to earn the win and Bernadina, Desmond and starting pitcher Tom Milone all cracked home runs for the Nationals, who bounced back after dropping the series opener on Friday.
Milone was called up from Triple-A Syracuse to make his major league debut and lasted 4 1/3 innings, giving up four runs on six hits while fanning two. Incredibly, Milone hit a three-run homer off Mets starter Dillon Gee on the first pitch he saw in his first major league at-bat in the second inning.
The Mets start former first-round draft pick Mike Pelfrey, who's three wins shy of reaching double digits for the fourth consecutive season.
The ninth overall selection by New York in 2005, Pelfrey won 13 games in 32 starts in 2008, then followed it up with 10 wins in 2009 and a career-best 15 in 34 games last season.
He won No. 7 this year on Aug. 24 in Philadelphia after scattering nine hits and three runs across six innings of a 7-4 triumph.
Pelfrey is 4-6 in 16 career starts against Washington with a 4.22 ERA and 50 strikeouts in 98 innings.
The Mets own a slim 7-6 edge in the season series with the Nationals.