The Mets got their first helping of humble pie with an epic meltdown in the eighth by their major league best bullpen, as Washington gave New York a taste of their own come from behind medicine.

“We can’t let this put us into a tailspin,” Mickey Callaway said.

Staked to a 6-1 lead, Jacob deGrom had the Nationals in the palm of his gifted right hand. Riding high on his seven-frame gem of an earned run on four hits, a walk and a dozen strikeouts, New York was closing in on their fourth consecutive defeat against their division rivals.

After surrendering an innocuous leadoff single to Moises Sierra, the ace in Callaway’s deck of cards fanned Michael Taylor, then lost Trea Turner on a 3-2 base hit to left. Seth Lugo traded places with deGrom and immediately loaded the bases with a four-pitch walk to Howie Kendrick.

Lugo was dispatched to the dugout for Jerry Blevins who blew his inheritance on an 88 MPH sinker that Bryce Harper deposited into right field for a two-run single, prompting Callaway’s fourth visit to the mound.

AJ Ramos was the answer for one batter, Ryan Zimmerman, who he fanned looking at an outside pitch framed beautifully by Jose Lobaton. Pedro Severino filled the bags with a two-out base hit to shallow left and Matt Reynolds avenged his former team with a free pass on four pitches to close the gap 6-4.

Callaway, brought in Jeurys Familia to stop the bleeding but the dominant closer was demoralized by Wilmer Difo’s game-tying single to right, then completely unraveled plunking Sierra, and plating the go-ahead run on a five pitch walk to Taylor.

“It’s one inning. It wasn’t even the game,” Callaway said. “We’ll learn from it and make sure that it doesn’t throw us into some kind of tailspin. Because we’re a really good team and we’ve been showing that.”

In the top of the ninth, Hansel Robles, who has been much better this season, tried to keep it a one run game, but his 94 MPH four-seam fastball to leadoff hitter Kendrick was at the wrong place at the wrong time, sailing into the center field seats.

On the Mets battered bullpen, “It was just unfortunate,” Callaway said. “Off night for a few of them. But we have to move on.”

How they respond to Monday’s loss is of utmost importance. If they come into Tuesday’s game with a fire under their rears and rebound, the Mets will be in good shape. If not, then they’re in trouble.