By the time the Mets finally rallied in the bottom of the eighth on Thursday night at Citi Field, it nearly triggered a flood of biblical proportions.

But after a 97-minute delay, the Mets completed their 2-1 comeback win over the last-place Nationals, as Mark Canha drove in the game-winning run with a bases-loaded sacrifice fly that knocked in Pete Alonso and Brooks Raley closed it in the ninth for the save.

The victory for a Mets team that had lost three of four and shown no signs of getting back into the playoff race, likely won’t change the organization’s mindset heading toward Tuesday’s trade deadline, but it was at least a sign of life at what had been a moribund Citi Field, with the Mets shut out until the eighth against a Nationals team that had won five of six.

Minutes after the Mets’ win, The Post’s Joel Sherman and Jon Heyman confirmed that closer David Robertson had been traded to the Marlins in exchange for two prospects — the No. 18 and No. 21 players in Miami system, according to MLB Pipeline — to mark the first sign of a sale.

Before that, Kodai Senga tossed six strong innings and gave up just one run on a pair of hits, but that seemed like it might cost him and the Mets the game, as Washington right-hander Josiah Gray — an All-Star this season — blanked them before leaving after six innings.

But facing Mason Thompson in the eighth, Jeff McNeil reached with one out on a dribbler in front of the plate that he beat out for an infield hit.

Alonso flared a single to center that sent McNeil to third.

Daniel Vogelbach then delivered a single to right to score McNeil and tie the game at 1-1.

Alonso and pinch-runner Danny Mendick advanced on a wild pitch by Thompson, who then hit DJ Stewart to load the bases for Canha.

But Washington replaced Thompson with Kyle Finnegan before Canha came to the plate, and that’s when the skies opened, causing the lengthy delay.

Canha delivered the sacrifice fly in front of the few thousand robust fans that remained after the stoppage in play.

The comeback came from nowhere, as the Mets created very little offense heading into the eighth.

With two outs and no one on in the bottom of the first, McNeil was drilled in the back for a second straight game.

He took a 95 mph Carlos Rodon fastball off his back on Wednesday, and Gray got him with a 90 mph cutter on Thursday.

The Mets loaded the bases with two outs in the second, but Brandon Nimmo flied out to deep left to end the threat and keep the game scoreless.

Senga, coming off a rough start in Boston, retired the first six batters he faced before Corey Dickerson led off the third with a single to right.

Senga stranded a pair of runners in the inning when he struck out Lane Thomas.

McNeil and Alonso both sent fly balls to the track in the bottom of the inning, but both came up short.

And they heard some boos when the fifth inning ended with a Francisco Lindor strikeout that turned into a double play when Nimmo was caught stealing.

The Nationals loaded the bases against Senga again in the sixth, this time with one out.

Keibert Ruiz delivered a sacrifice fly to drive in the game’s first run and Senga then hit ex-Met Dominic Smith with a pitch in the ankle to fill the bases for the second time in the inning, but got Dickerson to fly out to keep it a one-run game.

Washington threatened in the seventh with an infield single by Alex Call followed by a hit through the right side of the infield by CJ Abrams put runners on the corners, but David Peterson got a double play from Thomas.

With Gray out of the game after six innings, Brett Baty slammed a one-out double to right-center off Jordan Weems.

Omar Narvaez flied out to shallow left and Nimmo lined to left against lefty Jose Ferrer.

Peterson gave up a two-out single to Ruiz in the eighth and Ruiz advanced all the way to third on a wild pitch, but Smith grounded out.