Chad Tracy heard it has been almost exactly 10 years since Bryce Harper’s first major league game. So, the former Washington Nationals infielder did what people do nowadays long after they witness history.

He fired up YouTube.

Sure enough, everything about that night — April 28, 2012 — came flooding back. The mix of anticipatory cheers and reflexive boos with the second-inning announcement over the Dodger Stadium public address: “Coming to the plate ... making his major league debut ... left fielder ... number 34 ... Bryce Harper.” The overamped, violent swings that wrenched your back just from watching. The heat-seeking double over the center fielder’s head.

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And, who could forget, the mid-stride helmet-doffing as Harper rounded first base and chugged for second.

“I think he wanted everybody to see his face,” Tracy said by phone this week. “Everybody in the country was probably watching.”

Can it really be 10 years? Is it even possible? The Phillies superstar isn’t even 30, for crying out loud. He’s younger than 10 of his 28 teammates on the active roster entering the weekend. How is it that he has been in the majors longer than any of them save for 32-year-old reliever Brad Hand?

Harper celebrated one milestone this week when he reached 10 years of major-league service time, a mark attained by less than 10% of players, according to Players Association data. The Phillies presented him with a cake Tuesday night in Colorado.

Thursday will represent another occasion: the decadelong anniversary of his major league debut.

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“Looking back on it, I can’t believe it’s been 10 years,” said Harper, whose arrival in the majors coincided to the red-letter day with Mike Trout’s permanent return from triple A. “There’s just so many memories, from D.C. all the way to here. It’s crazy to think about. You look at the picture of 2012 and where I am now, it’s a lot different.”

And not only because Harper rocked a mohawk/mullet hairdo and wispy facial hair as a teenage phenom. His girlfriend then, Kayla Varner, is now his wife. He was 19 years, 195 days old in that first game, and as Tracy put it, “could’ve been one of our kids.” Now, Harper is a father of two children.

Oh, and there were times in 2012 when Harper acted his age. Take the Friday night in Cincinnati. Two weeks after getting called up, in the midst of an 0-for-5, three-strikeout game, he went down the tunnel leading to the Nationals’ clubhouse and swung his bat against a wall. It ricocheted back and hit his face, near his left eye.

“I’m down there trying to vasoline him up like he was a fighter, trying to get him to stop bleeding before he runs out there,” Tracy said. “It worked for a couple minutes, and then it was all down his face.”

The Nationals purposely gave Harper the locker next to Tracy, then a 32-year-old veteran in his eighth big-league season. Tracy had back-to-back 20-homer seasons for the Arizona Diamondbacks in 2005-06. But after playing in Japan in 2011, he was back in the majors trying to wring a few more years out of his career.

Tracy recalled a long conversation in spring training to lift Harper’s spirits after the Nationals sent him to triple A, a move that he said came as no surprise to anyone other than Harper.

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There were other lessons. Harper played one season in junior college in 2010 and for three minor-league affiliates after being drafted first overall. As former Nationals infielder Ryan Zimmerman told the Washington Post in 2016, Harper “kind of had to learn how to be a teammate.”

In reflecting this week on those formative years, Harper cited Tracy, Rick Ankiel, Xavier Nady, Mark DeRosa, and Jayson Werth as veteran role models. Tracy said they often encouraged Harper to be himself in the clubhouse. When Harper began getting cleats and other marketing swag sent to him, Tracy allowed him to take over a spare locker in between them that would typically belong to the longer-tenured player.

The Nationals also were protective of Harper. They rallied around him when Cole Hamels fired a fastball at his backside on May 6, 2012, a drilling that the Phillies ace startlingly admitted was intended as a welcome-to-the-majors baptism. And when a Toronto television reporter asked if Harper planned to celebrate a homer by taking advantage of Canada’s lower drinking age, they defended his memorable retort: “That’s a clown question, bro.”

But Harper’s teammates also made sure to check him whenever he needed a dose of humility.

“There were times he’d have a bad game and he didn’t want to talk to the media and he’d run out, and we’d have to be like, ‘You can’t do that, man. You have to talk to them when you have a good game and when you have a bad game,’ ” Tracy said. “There were teaching moments. We didn’t want anybody to mess with him, but we didn’t want him to be not humble enough. We walked that fine line with him.”

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So, yes, Harper has grown up before our eyes — and in the social media age, no less. But his playing style remains nearly the same.

That hair-on-fire aggressiveness in trying to seize an extra 90 feet? It still happens. Last year, Harper made 10 outs on the bases, one shy of his career-high in 2016. He still occasionally overshoots a cutoff man with his cannon-fire arm in right field, too.

It was natural in 2012 to wonder if it was all for show. Now, most people realize it’s just Bryce being Bryce.

“He’d hit a ground ball to second base and we’d say, ‘We love the effort, but you’ve got to play 162 [games] now, bud.’ Can’t leave your hamstring on first base over a ground ball to second,’ ” Tracy said. “But that’s what fans love about him. They love him throwing the helmet off on that first double. That’s always kind of embodied Harp. He likes the spotlight, but he plays really hard. People appreciate that.”

Harper doesn’t intend to change. He’s in the fourth season of a $330 million Phillies contract that runs through 2031. He won’t turn 30 until October. He figures he has a lot of baseball left and says he wants to play “until my body breaks.”

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That’s why it’s so mind-bending to think that Harper has been at this for 10 years. He said he was floored two weeks ago when an Oakland A’s player told him, “I grew up watching you play.” But he’s a generational player, like Ken Griffey Jr. in the ‘90s.

Consider this: Harper is only four years older than Phillies rookie center fielder Matt Vierling. But Vierling was a high school freshman when Harper reached the majors. J.T. Realmuto is a year older than Harper, yet he was in A-ball when the baseball world first fixed its gaze on No. 34 at Dodger Stadium.

Tracy thinks back to that night and finds the whole thing to have been so perfect, right down to the setting.

“To be in L.A., in the city of the stars, and to be getting your debut and being as big a star as you are at 19 years old, it just seemed very fitting,” Tracy said. “With Vin Scully announcing it and all of us being really excited to have him and knowing that a good career was going to happen, it felt like the stars really aligned. It definitely seemed a little different.

“And he’s turned out to be different. He’s won some MVPs, a multi-time All-Star, just a guy that’s had a very, very good career to this point. And he has a lot of time left, too.”

In the end, maybe that’s Harper’s biggest trick. To make us all feel old and somehow stay young.

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