WASHINGTON - On its face, the plan seemed so conveniently diabolical, even brilliant.

With the Mets set to face the Nationals in a crucial three-game series, Terry Collins arranged his pitchers so that the depleted leaders of the NL East would face three straight flamethrowers. Matt Harvey, Jacob deGrom, Noah Syndergaard -- in that order. Yes, it all seemed so neatly arranged, until it all backfired.

It didn't take long for things to go awry in Monday night's 7-2 loss to the Nationals, in which the Mets stumbled early and failed to regain their footing until it was too late.

DatabaseMatt Harvey's career starts

"We're all excited to play, and play here especially,'' said Harvey, who trailed 5-0 after his first three innings. "Unfortunately, I didn't get it going early.''

Harvey retired the final 14 batters he faced, though that served as little consolation. None of it could erase the sloppiness that haunted the Mets, long before the Nats put it away in the eighth on Ian Desmond's two-run shot against struggling Alex Torres.

In the first, Harvey botched a Danny Espinosa bunt and walked Bryce Harper, who was 0-for-12 against him. Both scored, with Harper coming in when first baseman Eric Campbell bungled a rundown.

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Things worsened in the third, when Clint Robinson slammed a two-run double over the head of centerfielder Juan Lagares. Robinson scored, making it 5-0, when third baseman Daniel Murphy forced a throw into the stands, the second of his two errors.

It hardly lined up with what Collins envisioned one day after the Mets prevailed in an 18-inning marathon against the Cardinals, one of their biggest wins of the season. The Nationals (50-41) moved three games ahead of the Mets (48-45).

Harvey (8-7, 3.19 ERA) allowed five runs (four earned) in seven innings. Although he hit a two-run single with the bases loaded in the fourth against Gio Gonzalez, pulling the Mets within 5-2, the momentum shift came after the damage was done.

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The Nationals started only three regulars, with Jayson Werth, Denard Span, Anthony Rendon and Ryan Zimmerman out of commission.

The Mets have been without David Wright and Travis d'Arnaud for almost the entire year, and Sunday's game compounded their issues. Soreness kept catcher Kevin Plawecki out of the lineup, and outfielder Michael Cuddyer was benched a day after a banged-up knee sidelined him. He still could wind up on the DL.

Still, the Mets deserved better for the way they swung the bats. "Actually, we had a chance to get back in it,'' said Collins, who watched the Nationals' suddenly stellar defense frustrate a Mets offense that showed signs of life.

Campbell spiked his helmet in the fifth, when he was robbed of what he thought would be a two-run triple to the gap thanks to a brilliant running catch by centerfielder Michael Taylor.

Earlier, Campbell was deprived of another hit, by third baseman Yunel Escobar. Escobar also made a nifty backhanded play in the first to snag what would have been a two-run double by John Mayberry Jr.

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A day after leaving 25 men on base and going 1-for-26 with runners in scoring position, the Mets left 10 and went 1-for-10 with men in scoring position.

"We're frustrated, obviously, but it's encouraging that we're barreling balls,'' said Campbell, who was victimized twice. "They're going to fall. We're going to score runs. But it is getting a little bit old.''