WASHINGTON - No matter the time, no matter the pitcher, if he's wearing a Mets uniform, he's an easy target for Nationals catcher Wilson Ramos.

On Sunday afternoon, Zack Wheeler was charged with slowing down the notorious Mets killer, an effort that once again proved futile in the Mets' 6-3 loss to the Nationals.

Entering Sunday afternoon's breezy series finale, Ramos owned a lifetime 1.051 on-base plus slugging (OPS) against the Mets, his highest mark against any team in the National League. And a struggling Wheeler proved he wasn't up to the task.

Ramos went 2-for-3 with a walk and four RBIs -- all of them against Wheeler -- who lasted just six innings.

Wheeler allowed five runs, though two were unearned, while striking out five and scattering six hits. He also walked two, putting him in a tie with the Phillies' A.J. Burnett for the second most free passes (26) in the National League.

In Wheeler's ninth start of the season, Collins hoped for a turning point, a clear end to a string of rough outings.

Before the game, Collins insisted he was "not yet" concerned about Wheeler's pedestrian results. He focused instead on the pitcher's raw ability. So long as Wheeler can keep the ball near the strike zone, Collins figures he has a chance of getting outs.

"The real good ones, they find it, they figure it out," Collins said. "And I think he'll figure it out. I really do."

That day was not Sunday.

The Mets gave Wheeler a 1-0 lead in the second on Juan Centeno's RBI single to score Lucas Duda, who settled for a leadoff double when his drive hit the top of the right centerfield fence.

Ian Desmond tied it with one swing in the second, bashing a solo shot that sailed into the stands in leftcenter, easily clearing the Mets bullpen. The tie didn't last long.

Mets shortstop Ruben Tejada extended the third inning when he tried backhanding Jayson Werth's grounder only to have the ball pop out of his glove. Following the two-out error, Ramos ripped a double to left, pushing the Nationals' lead to 3-1.

Wheeler (1-4, 4.53 ERA) scuffled again in the fifth inning, when Ramos again made the Mets pay dearly. With one out and the bases loaded, Ramos delivered a two-run single, giving the Nationals a 5-1 cushion.

The Mets chipped away with two runs in the sixth on run-scoring singles by Juan Centeno and Juan Lagares, who started his second straight game in centerfield.

But for the second time in the game, the Mets ran themselves out of an inning, this time when Centeno was caught trying to advance to second base after his single. In the first, Murphy stunted a potential rally by straying too far from third base, allowing Desmond to throw behind him and record the final out of the inning.

In the eighth, the Nationals added an insurance run by scoring their third unearned run of the game. After walking, Ramos moved to second on a passed ball charged to the catcher Centeno, who had earlier made a throwing error.

Ramos later scored on a fielder's choice, bumping the lead up to three runs. Closer Rafael Soriano worked a perfect ninth to cap off three shutdown innings by the Nationals bullpen.

Nationals starter Jordan Zimermann (3-1 3.70 ERA) allowed eight hits but just three runs in six innings to beat the Mets (20-23), who enter Monday's off day with losses in four of their last five games.