WASHINGTON - Terry Collins didn't bother trying to downplay the importance of this three-game series for the Mets. He embraced its ramifications.

Enough was at stake for the manager to save his biggest weapons for the Nationals, lining up the lethal triumvirate of Matt Harvey, Jacob deGrom and Noah Syndergaard.

"We set the rotation out of the break pretty much pointing at this series knowing that we've got to beat these guys,'' Collins said, before watching the Mets fall behind early in Monday night's 7-2 loss to the Nationals.

Harvey (8-7, 3.19 ERA) retired 14 straight to conclude his seven innings, but he gave up five runs (four earned) in his first three.

He hit a two-run single with the bases loaded in the fourth against lefty Gio Gonzalez, which got the Mets within 5-2. But the momentum shift came far too late against the Nationals, who made it 7-2 in the eighth on Ian Desmond's two-run shot against struggling Alex Torres.

The Nationals (50-41) moved three games ahead of the Mets (48-45) in the NL East. A day after leaving 25 men on base and going 1-for-26 with runners in scoring position in an 18-inning win at St. Louis, the Mets stranded 10 and went 1-for-10 with men in scoring position.

This series is a test of which side is better equipped to handle injuries. Both clubs know their way around an MRI tube. The Nats 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.

Sunday's marathon compounded the health issues. Soreness kept Kevin Plawecki out of the lineup. Michael Cuddyer was benched a day after a banged-up knee sidelined him.

The depleted Mets didn't get much luck. Although they forced Gonzalez to labor, they were undermined by brilliant defense by the Nationals, highlighted by Michael Taylor's running grab in the right-centerfield gap in the fifth. Eric Campbell slammed his helmet into the dirt, fuming when his potential two-run double became just another out.

Nats third baseman Yunel Escobar made a sprawling, backhanded play to rob John Mayberry Jr. of a two-run double in the first. In the second, Escobar took away a hit from Campbell. Bryce Harper's sliding catch in right robbed Wilmer Flores, and Mayberry saw catcher Jose Lobaton reach over the railing to end his at-bat in the eighth.

It was all too much for the Mets, who found themselves down 5-0 after three innings -- their punishment for sloppiness.

In the first, Harvey failed to field Danny Espinosa's bunt before walking Harper, who had been 0-for-12 against him. Escobar lashed a run-scoring single, then alertly got into a rundown after being caught trying to advance on a ball in the dirt. In the chaos, the Mets neglected to keep tabs on Harper, who scored from second before Escobar finally gave himself up.

Still, the Nationals didn't take control until pushing across three runs in the third against Harvey, who revealed his frustrations one eye roll at a time. He sulked after walking Harper for a second time, once again following an Espinosa hit. Two batters later, Clint Robinson's two-run double made it 4-0.

The Mets' defense burned them again in the third, when third baseman Daniel Murphy fielded Desmond's roller and fired it into the seats. Robinson scored, leaving the Mets in a deeper hole.