On Thursday in New York, Ian Desmond registered the first five-hit game of his career and drove in three runs, as the Nationals beat the Mets, 10-1, to extend their winning streak to five games.
Washington's Tom Milone (1-0) earned his first career win, limiting New York to a run on three hits and three walks in 5 2/3 innings.
The Nationals swept a four-game series in Flushing, N.Y., for the first time since the Montreal Expos won all four meetings at Shea Stadium from September 2003.
Lannan, an eight-game winner last season, has lost five of his last six starts in 2011, including a 9-3 loss to Houston on Sept. 10. The 26-year-old was touched for six runs in eight hits in just 2 1/3 innings against the Astros, five days after he'd beaten Los Angeles, 7-2.
Lannan is 2-4 in eight lifetime starts against the Marlins, including a 5-2 loss in Washington on July 28.
Washington is 4-6 in his last 10 starts.
On Thursday in Philadelphia, Hunter Pence and Raul Ibanez both had first- inning RBI doubles to back five solid frames from Kyle Kendrick, as the Phillies downed the Marlins, 3-1, in the opening game of a doubleheader.
In game two, Ryan Howard's RBI double in the bottom of the 10th scored Michael Martinez with the winning run, as Philadelphia pulled out a 2-1 victory.
Going for the Marlins tonight will be Puerto Rican veteran Javier Vazquez, who aims for a fourth straight win and can exceed 10 wins for the 10th time in his career.
He last went past 10 wins in 2009, when he was 15-10 with Atlanta. He was 10-10 with the New York Yankees in 2010 over 31 appearances.
Vazquez is 2-2 in five career starts against the Nationals with a 4.09 ERA in 33 innings.
He's 6-4 in 16 road starts in 2011 and the Marlins are 6-4 in his last 10 appearances overall.
Florida is 8-4 versus the Nats this season.