Brandon Moss went 3-for-5 with a pair of doubles, drove in two runs and scored three times. Shortstop Jed Lowrie was 2-for-4 with his 12th home run of the season - a two-run job - drove in four runs and scored twice.
The win tied the series at a game apiece with the rubber match set for Thursday afternoon at 1:10 pm EDT in Minnesota.
Having won seven of their last ten while the Rangers went 2-8 has opened things up in the AL West, but the A's still have 17 games on the schedule before they can claim the unlikely (at the start of the season) prize of AL West champs.
Haren threw for six full innings, allowing just one hit - a fourth-inning leadoff single by Juan Lagares - one walk, fanning eight. He threw just 86 pitches before being lifted for a pinch-hitter in the seventh with a 1-0 lead.
The Nats scored a pair in the eighth to insure the lead. Manager Davey Johnson used three relievers before bringing in close Rafael Soriano, who allowed a hit in the ninth inning but kept the Mets off the board for his 41nd save, second in the NL, behind Atlanta's Criag Kimbrel.
The Nationals will look to make it four straight over their hosts when the two teams meet at Citi Field, 1:10 pm EDT.
Today's Trivia: Only one time has a player hit at least 50 home runs and 50 doubles in a single season. Who was it?
Yesterday's Answer: Mike Schmidt led the NL in home runs a record eight times. Barry Bonds only led the league in homers twice.