WASHINGTON — The goal for the rest of the first half is far from aspirational. The Mets are hurting too much to hope for anything more. Terry Collins has said as much.

It’s about survival.

But these days, even treading water appears to be too much to ask of these Mets, 5-0 losers on Tuesday to the Nationals.

Rain postponed first pitch by an hour. And with one out in the bottom of the fourth, another passing storm halted play for 1 hour, 25 minutes. It was long enough to prematurely end an intriguing pitching matchup between the Mets’ Matt Harvey and the Nationals’ hyped prospect Lucas Giolito in his big- league debut.

But when play resumed, Bryce Harper wasted little time altering the course of the game, lining a two-run homer off lefty specialist Jerry Blevins to give the Nationals a 3-0 lead.

It was the first homer Blevins allowed to a lefty since Prince Fielder hit one in 2013.

Familiar Mets tormentor Wilson Ramos lined a two-run double off the centerfield wall in the seventh inning to give the Nationals a 5-0 lead.

Once again, the Mets endured a bitter cocktail of incompetence at the plate and bothersome injuries.

The Mets loaded the bases with one out in the sixth, when they trailed 3-0. But a ghost from their past — Oliver Perez — excelled in his second-coming as a lefty specialist.

Perez got James Loney flailing at a slider before Wilmer Flores hit a harmless flyout to leftfield. It was the Mets’ best chance to make something of what became another lost night.

Perez was credited with the victory.

Meanwhile, Curtis Granderson left the game when play resumed in the bottom of the fourth. The Mets did not divulge a reason except to say he had trouble getting loose after the delay. Earlier in the frame, he banged into the rightfield wall making a catch on Ramos’ fly ball.

In the seventh, Mets reliever Hansel Robles needed help getting to his feet when he took a Ryan Zimmerman liner off his right leg. The ball bounced to second baseman Neil Walker to end the inning. But Robles looked rattled as he limped off the field.

The Mets (40-36) dropped five games back of the Nationals (46-32). And to avoid dropping six games behind, they need spot starter Logan Verrett to outmatch the Nationals’ ace Max Scherzer.

The Mets had hoped to get a critical start from Harvey (4-10). But the rain cut his night short. He allowed only one run — on Anthony Rendon’s triple — in 3 2⁄3 innings..

Giolito, 21, tossed four shutout innings, which came after the Nationals sent Stephen Strasburg to the DL with a back injury.

Notes & quotes: Lucas Duda will resume baseball activities in two weeks. He has been dealing with a stress fracture in his back, general manager Sandy Alderson said . . . The Mets are still determining a new timeline for the return of Zack Wheeler, whose rehab from Tommy John surgery had been pushed back because of nerve irritation in his elbow . . . Prospects Dilson Herrera and Dominic Smith will represent the Mets at the Futures’ Game during all-star game festivities in San Diego.