New York Mets' Michael Conforto, left, walks off the field...

New York Mets' Michael Conforto, left, walks off the field past Washington Nationals catcher Yan Gomes after striking out swinging in the fourth inning of a baseball game, Wednesday, May 15, 2019, in Washington. Washington won 5-1. (AP Photo/Patrick Semansky) Credit: AP/Patrick Semansky

WASHINGTON — What might have been the biggest Mets at-bat of their 5-1 loss Wednesday to the Nationals came early enough that it was hard to recognize in the moment as a critical juncture.

Top of the third. Two-run Washington lead. Two outs, two runners in scoring position. Robinson Cano at the plate.

Nationals lefthander Patrick Corbin gave Cano a 2-and-2 slider over the middle of the plate but a tad down in the strike zone. Cano weakly hooked it toward first for a routine inning-ending grounder. Minutes later, Washington continued their assault on Wilmer Font, including Victor Robles’ homer on the second pitch of the inning.

The Mets had two hits and no runners in scoring position the rest of the night.

Cano finished 0-for-4 with three strikeouts. He was far from the only offender for the Mets (20-21), but he might have been the most predictable, given how his season has gone.

Cano is hitting .245. His OPS is .672. It’s even uglier against lefthanders: .119 with no extra-base hits in 46 plate appearances.

He hasn’t homered since April 21 (63 at-bats ago). Before that, April 6. Before that, Opening Day. His three long balls are one more than Noah Syndergaard, a pitcher with 23 plate appearances.

“I feel good at the plate,” Cano insisted before relenting. “I don’t want to say it’s not falling, but sometimes I’ve been missing my pitches. The past couple of games, I’ve been missing fastballs right down the middle.

“For a hitter, when things aren’t going your way, that’s when you know — you’re missing your fastball right down the middle.”

So far, manager Mickey Callaway has refused to move Cano out of the No. 3 hole in the Mets’ lineup, even against a tough lefty like Corbin. The Mets reserved that spot for Cano, 36, immediately upon acquiring him from the Mariners in the blockbuster December trade, their signature offseason move.

Cano has shown signs of returning to his regular form — a four-hit game last week in San Diego, a two-hit game a couple of days later — but hasn’t been able to find any real traction at the plate. He is hitting .191 in May.

“(Third) a good spot for him,” Callaway said. “I’m not saying he’ll always stay there. But right now, I think we give him a chance to break out of this a little bit.

“Historically, he’s a Hall of Fame-type player, so there’s always going to be high expectations on Robbie. … If anybody knows how to fix it and fix himself, it’s going to be Cano. He’s been doing this for a very, very long time. He knows himself. He knows his swing.”

Font got smacked around for five runs in 2 1/3 innings. The Nats scored thrice in the first inning, including on Anthony Rendon’s booming double to center, and twice in the third, including on Robles’ homer. Half of Robles’ eight homers this season have come against the Mets (eight games).

Which of Font’s pitches weren’t working?

“They were all bad,” he said through an interpreter.

Font’s flop looked even worse compared to Corbin, who allowed one run and struck out 11 in eight innings, his longest outing in his debut season with the Nationals. He got 12 whiffs on his slider, which Callaway called “one of the best pitches in the major leagues.”

“I would say he’s got two sliders,” Cano said. “One to throw for a strike and one he throws to make you chase. And both of them look the same.”

Reliever Drew Gagnon (2 2/3 scoreless innings) picked up his first major-league hit, a single to center off of Corbin. That was one of four Mets hits in the game.

“The score wasn’t outrageous,” Callaway said. “But it didn’t feel like we were in the ballgame because of what Corbin did.”