Submission came after an assault on his senses. With every crack of the bat, with every liner that hissed through the air, with every boo and curse that tumbled down from the stands, his resolve grew shakier.

Matt Harvey couldn’t take it anymore.

So when Terry Collins made his merciful walk from the dugout in the third inning Thursday night, the brooding pitcher met his manager a few steps before he reached the mound. Harvey quietly handed over the baseball, stalked through the dugout and disappeared down the steps to the clubhouse.

Rock bottom had arrived, cloaked in a bitter 9-1 loss to the Nationals that sent the Mets scrambling to answer a few vexing questions.

What has happened to Harvey? What’s next? A few days off to recalibrate? A trip to the phantom disabled list with a bruised ego?

Nobody knows, of course, so the public deconstruction of what appeared to be a generational talent continues unabated.

The final line: a career-low 2 2⁄3 innings, a career-high nine runs (six earned), eight hits, two strikeouts.

The Mets trailed by eight runs in the third when Collins finally had seen enough. The only two outs of the inning came on a 400-foot flyout and a weak grounder by Stephen Strasburg.

There was a time when Collins would have had to pry the baseball from Harvey’s hand. There was a time when Harvey would have sprinted from the dugout to the pitcher’s mound. There was a time when the fans here mocked Strasburg with chants of “HAR-VEY’S BETTER!”

On Thursday night, there was only the flood of thousands of boos and one no longer larger-than-life persona.

Harvey, 27, had offered hints of the bottom falling out. Like sneak previews before the feature event, scenes foreshadowed his doom. Red flags emerged from all but one of his first eight starts. He no longer missed bats. He no longer commanded his arsenal. He no longer lit up the radar gun late into the night.

He no longer was himself, an unflattering reality that the Nationals reinforced with glee.

In issuing his latest vote of confidence before the game, Collins hoped that Harvey would rise to the occasion the way he’s done so many times in the past. Adrenaline, the manager hoped, would make the difference. The Mets needed Harvey to pitch well to avoid dropping two of three to their rivals.

That hope disappeared four batters in when old friend and new tormentor Daniel Murphy punished a mistake. Ahead in the count 0-and-2, Harvey flipped a curveball that spun helplessly over the plate, and Murphy hit a two-run homer to center.

Harvey turned to watch the flight of the ball, then blinked when it disappeared over the fence.

It only got worse. The Nationals scored seven runs in the third, when Harvey’s teammates didn’t give him the help he desperately needed. Steady shortstop Asdrubal Cabrera couldn’t make a clean transfer. Leftfielder Michael Conforto couldn’t grab a liner. Centerfielder Yoenis Cespedes couldn’t cut off a ball in the gap.

Anthony Rendon cracked a 106-mph rocket for a two-run double. Wilson Ramos hit a two-run single, a 108-mph screamer. Restless fans squirmed, then groaned, then booed.

In the scouts’ section, talent evaluators described a stranger. Harvey’s pitches lacked life, sharpness, movement. One concluded with this stinging epithet: “The hitters are not fearing him.”

Three batters later, Ben Revere delivered a two-run triple that extinguished the final traces of fight from The Dark Knight.

By the time Collins stepped onto the crushed dirt of the mound, Harvey’s ERA had climbed to 5.77 and his record was on the way to 3-6.

Harvey’s next start is supposed to fall against these same Nationals in Washington, on the same stage he used last year to return from Tommy John surgery. Now, based strictly on results, that appearance is far from a given.