J.D. Martinez speaks at a news conference during Mets spring...

J.D. Martinez speaks at a news conference during Mets spring training on Saturday. Credit: Newsday/Tim Healey

PORT ST. LUCIE, Fla. — Ten years and one day later, back in an office with David Stearns for another key conversation near the end of spring training, J.D. Martinez had to laugh.

Stearns was the assistant general manager for the Astros in 2014 when they released Martinez days before the season began. Back then, he hadn’t come close to establishing himself as a big-leaguer. He was a 26-year-old corner outfielder ticketed for the minors — until Houston decided it didn’t even want him there.

Now Martinez is one of the best designated hitters in baseball and a massive last-minute addition for the Mets and Stearns, their new president of baseball operations. He’ll bat fourth, right behind Pete Alonso, manager Carlos Mendoza said Saturday, which was Martinez’s first official day with the team after signing a one-year, $12 million contract.

That little life-changing move a decade ago? Stearns said he was of a mind to at least keep Martinez in Triple-A, not drop him outright, but the final call wasn’t his.

Martinez, a six-time All-Star, is glad it went down the way it did.

“We joked about it,” said Martinez, who wound up breaking out with the Tigers in 2014. “I said, ‘Last time I came in this office with you, it didn’t end well.’ He said, ‘Oh, that was a long time ago. Big mistake!’

“It’s cool. It was a blessing. At the time, it was the worst thing to me. And I felt like the world was falling down on me. But then I looked back and you know, God has got a reason he does everything, and that was the biggest blessing for me ever. So I said thank you.”

Stearns added with a laugh: “Wild baseball world. Bad decision.”

Together again, Stearns is looking for Martinez to be for the Mets exactly what he has been for the Tigers, Diamondbacks, Red Sox and Dodgers: a provider of thump and wisdom.

The first of those will have to wait. He’ll need at least 15 days — the first week and a half of the season — to get ready for major-league action, Mendoza said.

During his long offseason, Martinez kept busy by working out at his alma mater, Nova Southeastern, and embracing the Fort Lauderdale pickleball community, but neither was as good as a true spring training would have been.

Instead, he’ll have to embark on his own abbreviated camp, which began Saturday when he took a few rounds of batting practice and stood in on Adrian Houser’s bullpen session to track pitches. When the Mets break camp Sunday, Martinez will remain in Port St. Lucie indefinitely.

“I’ve been lifting, hitting, running,” he said. “But it’s one of those things where it doesn’t take the place of actual baseball. It’s kind of weird. You can train as hard as you want all offseason, but nothing gets you ready like actual baseball . . . The last thing I want to do is rush through it and get hurt. I want to make sure I take it slow and build my body up to get back out there.”

Mendoza gave up his jersey number, No. 28, when Martinez asked. His only request after deciding to switch to No. 64, his old Yankees digits: “Hit a lot of homers.”

“We gotta keep him healthy,” Mendoza said. “If he needs more at-bats, we’ll give him more at-bats. If he needs to go play with one of our affiliates, he’ll do that too.”

Martinez’s other major skill — dispensing advice as a “hitting savant,” in Alonso’s words, or a “special hitter,” as Mendoza called him — already has started to take effect. He said he told teammates he is “an open book” and that they shouldn’t “ever be intimidated or scared to come up to me.”

In a fleeting moment ripe for awkwardness, Martinez approached Mark Vientos during batting practice, throwing an arm around his shoulder and initiating a chat. They know each other a bit because they have worked out at the same South Florida facility in recent offseasons, Martinez said.

Vientos was penciled in as the Mets’ DH until the final half-week of spring training and has been plainly disappointed the past couple of days. Martinez took his job, so his fate is unclear.

Martinez’s message: It’ll all be OK. He spoke from experience, knowing what it is like to toil in your mid-20s with the franchise that drafted you.

“We kind of talked a little bit on how I understand his position,” Martinez said. “He’s a young kid. He’s 24 years old. He’s got so much time in this game. He’s got so much talent. I understand his frustration.

“I was like, you know, there’s plenty of opportunities, whether it’s here, whether it’s another team. You just go out there and you play your game and you play your hardest and the chips are gonna fall. Talent will always find its way to the big leagues.

“I gave him my example of my career and he understood it and I was like, there’s no reason to be mad about or upset about it. It’s just look at it and use it as focus. He was open-minded about it. He was fine about it, honestly.”

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