WASHINGTON — Matt Harvey sat in his manager’s office last week and asked for another chance. He couldn’t promise that his fastball would sizzle or that his slider would bite. He couldn’t guarantee what his arm would produce from pitch to pitch.

This, of course, has been at the crux of his demise.

The embattled righthander nevertheless flashed his trademark brashness and insisted on the opportunity to pull himself from his tailspin. But when his chance came Tuesday night, and he got used as a piñata in the Mets’ 7-4 loss to the Nationals, Harvey left others to answer for the latest chapter in his free fall.

Harvey was chased after surrendering five runs and eight hits in five innings. He walked two and struck out only one, his lowest total in 75 big-league starts. His velocity waned, following a familiar script, leaving the Mets little chance on a night dominated by the Nationals’ Stephen Strasburg (8-0).

The Nats slammed five homers — three against Harvey — who fled the clubhouse before addressing another alarming outing. It only added credence to the lingering belief that his confidence has been rocked.

“He’s frustrated,” catcher Kevin Plawecki said. “I’m frustrated, just because I want to help him out as much as I can. It’s just one of those things where you’ve just got to keep grinding through and keep working to get better.”

Terry Collins, a steadfast public defender for Harvey, acknowledged that the Mets may be better off with him not pitching.

Again, Collins did not commit to Harvey making his next start. Instead, he will huddle with general manager Sandy Alderson and pitching coach Dan Warthen to plot the next move.

“We’ve got to think what’s not just best for Matt, but what’s best for us moving forward at the moment,” Collins said. “So there’s a lot of things to consider. We’re not going to make any rash judgments tonight. We’re going to sleep on it and talk about it tomorrow.”

Though it had been brought up as a potential option, little appetite appears to exist within the organization to demote Harvey to the minors, where he could work on his issues. Other options included placing him on the disabled list or skipping his next outing to buy more time.

Harvey cratered in his previous outing, a nine-run (six earned) public dissection by the Nats in 2 2⁄3 torturous innings. Still, the Mets accepted his plea and kept him in the rotation. They’d pay for it.

Ryan Zimmernan and Anthony Rendon slammed back-to-back homers in the fourth, on changeups that Harvey carelessly left over the plate. But it was an old ally, Daniel Murphy, who beat Harvey into submission with a two-run shot into the upper deck in the fifth.

Murphy knew it right away, holding his pose, his bat held in front of him after returning it from his follow through. He began his trot around the bases with two joyous hops, allowing the sensation of sweet-spot contact to wash over him.

Harvey (3-7) stewed in his familiar misery. He looked over his left shoulder, then snapped his head away, sparing himself the sight of watching his 94-mph fastball disappearing.

When his spot came up to lead off the sixth, Harvey was lifted for a pinch hitter, a no-brainer.

By the end of the night, Harvey’s fastball faded from 96 mph to 93. Mockery poured down from the stands. “Har-vey! Har-vey!” the fans called out, taunting him on a night in which he looked tentative.

Of the 105 qualified starting pitchers in the major leagues, his 6.08 ERA ranks 101st.

“I’m pretty surprised,” Collins said. “I’m really surprised. This guy’s too good, he’s just way too good to continue like this.”