WASHINGTON — Pinch-hitting with any regular degree of success requires discipline, the kind that is usually gained through the years. It’s why Mets manager Terry Collins believes that the assignment is typically reserved for players with experience.

In Brandon Nimmo, the Mets might have an exception.

“For a young guy coming off the bench and doing what he’s done, he’s been pretty good,” Collins said on Wednesday, before the Mets’ series finale against the Nationals was postponed by rain. “It’s a tough role for young guys to do. But he pays attention.”

Nimmo, 24, has played in just 47 big league games since he was first called up last season. In that span, he’s a .290 hitter with a homer and eight RBIs in 93 at-bats. But he has excelled in his opportunities off the bench.

As a pinch-hitter, Nimmo is 9-for-19 in 23 games, a slash line of .474/.565/.526. It’s hardly a large enough sample size to declare him a specialist. But it has been enough for Collins to take notice.

Nimmo’s simple swing, the manager said, may be behind some of the outfielder’s success off the bench in his limited chances thus far.

“He’s going to be a good player, he’s going to be a good hitter,” Collins said. “(He) hits the ball all over the field. He’s done well.”

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Overall since his promotion from Triple-A Las Vegas on June 16, he is hitting .350 with a double and two RBIs in 15 games. That average went up in Tuesday’s 11-4 loss to the Nationals, when he recorded a career-high three hits.

Meanwhile, he has rolled along with his early success as a pinch-hitter. After going 6-for-12 in such scenarios last season, Nimmo is 3-for-7 in his pinch-hit chances this year.

“I don’t know the exact recipe for it but I think it’s being willing, willing to help the team in whatever way and accept your role, whatever that may be,” Nimmo said. “I try to not complain or get upset about things I can’t control.”

Entering the season, the Mets envisioned the former first-rounder Nimmo coming off the bench. With Michael Conforto looking like he’d begin the season with Triple-A Las Vegas, Nimmo appeared to have a spot on the Opening Day roster.

The World Baseball Classic changed those plans. Playing for Italy, Nimmo injured his hamstring, which sidelined him at the end of spring training. Later, his rehab was complicated when a nerve issue developed in his thumb.

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Eventually, Nimmo made it back, and the timing of his return proved particularly helpful this week. With Juan Lagares on the disabled list after undergoing thumb surgery, Nimmo got the call.

And when veteran Curtis Granderson was sidelined by stiffness in his right hip, it was Nimmo who stepped in to play centerfield. He has held his own at the position, even though scouts have long believed he’s best suited to play at the corners.

Either way, early in his big-league career, Nimmo has shown signs that he can be a productive player off the bench.

“I just try to be ready to help these guys however I can,” he said. “I think that goes into the preparation and the mindset going into it. But that’s the biggest thing. After that, there’s some luck that goes into baseball, so some things have gone my way sometimes and that’s been great. Sometimes, they haven’t. But I’ve had an even keel about it.”