Dmitri Young started the inning with a walk from Kevin Gregg (0-5). After Austin Kearns struck out, Wily Mo Pena singled to put runners at the corners. Ronnie Belliard fouled out on a bunt attempt, but Flores followed with a double off the left field wall.
Ryan Zimmerman and Kearns each drove in a run, while Chris Schroder (2-1) got the win for pitching a scoreless ninth for the Nationals, who have won four straight.
Mike Jacobs went 3-for-4 with an RBI for the Marlins, who have lost four of their last six games.
Miguel Cabrera had an RBI for Florida. It was No. 500 in his career, making him the third youngest player to reach 500 RBI at 24 years and 139 days, trailing just Mel Ott (23 years, 74 days) and Ted Williams (24 years, four days).