WASHINGTON — The 1,000th strikeout of David Robertson’s career came Friday night on a 92.4-mph cutter to Nationals outfielder Alex Call.

For his first, 15 years earlier, Robertson used a cutter nearly 3 mph slower — 89.7 — as a Yankees reliever to strike out Mets pitcher Oliver Perez at Shea Stadium.

It took Robertson 746 games to touch four digits in strikeouts and become just the fourth active reliever to reach the milestone. As a 15-year veteran playing with his sixth team, the 38-year-old is somehow throwing harder than he did as a 23-year-old kid in pinstripes.

In a clubhouse filled with higher-profile pitchers attempting to conquer age, such as Max Scherzer and Justin Verlander, the most successful Mets pitcher fighting Father Time, at least early in the season, has been Robertson, their closer.

“I got a new elbow. That helped a lot,” said Robertson, who underwent Tommy John surgery in 2019 and missed the 2020 season. “I was definitely not going to get through without that surgery.

“I just try to stay in shape. Try to keep a positive attitude. And when I get in between the lines, do everything I can to try to get those outs.”

Robertson has been successful through a sterling start to the season, in which he has done his best Edwin Diaz impression.

Robertson, who did not pitch Saturday after the Mets-National game was suspended until Sunday after a nearly four-hour rain delay, has allowed just one earned run in 17 innings (0.53 ERA) and converted seven saves.

He couldn’t make it eight Friday night, when he recorded five outs, but walked two in the ninth inning before giving way to Drew Smith, who earned his first career save.

But Robertson still was untouchable in the process and added four more strikeouts to his ledger, including the milestone.

“It’s a big number I’ve been chasing for a while. I wasn’t sure if I was ever going to get to it or not,” said Robertson, who signed a one-year, $10 million pact with the Mets this offseason. “I look at it like it’s a number of the accomplishments that Scherzer and Verlander got. When they get to 3,000 [strikeouts], I feel like getting to 1,000 as a reliever is a big deal.”

He is just the 14th pitcher in MLB history to record as many strikeouts solely in relief, and Robertson’s only active company are Kenley Jansen, Craig Kimbrel and Aroldis Chapman.

Advancements such as surgeries and pitching technologies have made it easier to age as a pitcher, and the Mets — fronted by age-defying starters Scherzer and Verlander, who are a combined 78 years old — hope to be the beneficiaries.

“We don’t really think of ourselves as being old,” said Robertson, who has 164 career saves. “We’re competitors. I still feel like I’m at the top of my game, and I think they do, too.

“We’ll continue to pitch until the game lets us know or until our wives tell us we can’t do it anymore.”

Manager Buck Showalter is not using Robertson like a frail, old arm.

The Mets’ best healthy reliever threw 40 pitches Friday in his second outing of multiple-inning work. Showalter acknowledged he doesn’t want to stretch Robertson like that “very often,” but the bullpen was short and there was a game to win.

After Smith struck out Washington’s Lane Thomas to preserve the victory, Robertson said he hung out with a few of the guys and drank some beer to celebrate.

Robertson came to the Mets with hopes that he would be celebrating with champagne late in the season. His only World Series ring was won with the 2009 Yankees.

“I would like to end it on a high note. I would like to end it [at some point] on a World Series,” Robertson said. “That’s my goal.”