The Mets' Mark Vientos rounds the bases after hitting a...

The Mets' Mark Vientos rounds the bases after hitting a solo home run during the second inning of a spring training game against the Cardinals March 1 in Jupiter, Fla. Credit: AP/Jeff Roberson

TAMPA, Fla.

Around 10:30 a.m. Friday, there was euphoria in the visiting clubhouse at Steinbrenner Field, where Pete Alonso and Francisco Lindor raved about the pending arrival of DH extraordinaire J.D. Martinez.

Fast-forward to 3 p.m., midway through the seventh inning of the Mets’ 5-3 loss to the Yankees, and it was a much different scene. Mark Vientos, still in uniform, did not express the same unbridled enthusiasm about the Martinez signing as his teammates had.

Nor did anyone expect him to. Vientos spent the past 5 1⁄2 weeks, right up until Thursday night, believing that the Mets were planning to go with him as the team’s everyday DH. They had not given him any reason to think otherwise.

The Mets’ narrative in spring training was all about evaluating their younger players, with new president of baseball operations David Stearns on board. And from that process would spring an opportunity for Vientos, who never really got a legit shot last season under the Billy Eppler administration.

Nothing was written in stone, of course. But as long as the Mets resisted the temptation to bring in a more proven bat, each passing day could be read as another vote of confidence for Vientos or a growing willingness to roll the dice on his power potential.

But that sort of commitment is a tenuous one in this business, and it all but evaporated Thursday when Steve Cohen’s slow-play with agent Scott Boras paid off in a heavily deferred one-year, bargain-rate $12 million deal for Martinez.

Martinez showing up was the competition Vientos couldn’t win. He’s a six-time All-Star and multiple Silver Slugger DH coming off a 33-homer, 103-RBI season for the Dodgers.

Vientos said his agent notified him by text Thursday night, and after manager Carlos Mendoza took him aside the next morning for a pep talk, the best Vientos could muster for the media was a sullen series of answers to the anticipated round of questions.

“Nice,” the deadpan Vientos said of the Martinez pickup. “Good for the team.”

Such is the flip side of importing a big-name veteran hitter: the sound of a prospect’s dream crumbling before his eyes.

It’s not the end for Vientos. With Martinez consenting to a week or so in the minors to get up to speed, that should buy Vientos time at DH for the big club — if the Mets don’t trade him before Opening Day. But now the clock will be ticking on his return to Triple-A Syracuse, and once he’s back down, Vientos is going to need some help to boomerang up to Flushing again.

That’s an incredibly discouraging turn of events for someone like Vientos, whose perpetual smile during spring training was reflective of the long-awaited chance he seemingly had been granted.

Technically, Vientos was competing side-by-side with Brett Baty, but the original 2024 blueprint was for Vientos to assume DH duties and Baty to get another shot as the starting third baseman.

Now his buddy Baty stays on the major-league track and Vientos is only marginally better off than he was a year ago. That’s tough to swallow, which is why Mendoza checked in with Vientos before Friday’s game.

“The biggest thing with Mark is just continue to do the things he’s been doing,” Mendoza said. “And opportunities will arise. I know it’s hard. Vientos is a huge part of our future here and the present, too.”

Right on cue, Vientos followed up that chat by going deep in his first at-bat, smacking a 97-mph fastball from Yankees starter Luis Gil over the rightfield wall. It was a team-leading fifth homer for Vientos, who is hitting .222 (12-for-54) with a .787 OPS.

When it comes to Grapefruit League stats, the significance is in the eye of the beholder. But for Vientos, someone whose calling card is loud contact, he was making the right kind of noise.

“The opportunity that I got,” Vientos said, “I feel like I made the most of it.”

Was there anything else he could have done to fend off the Martinez signing? Probably not. No matter how much Vientos raked in March, he was never going to be a better one-dimensional, bat-first player than Martinez, 36, a career .287 hitter with an .874 OPS who is considered to be among the best at the DH gig.

“He’s a stud,” Alonso said. “He can change the game with one swing of the bat and he’s really dynamic at the dish.”

The number that eventually doomed Vientos had nothing to do with the boxscore. It was the plummeting price tag for Martinez, whom some projected to get a two- or three-year deal worth $20 million annually when free agency began.

That the Mets were able to get him at such a steep discount, nearly half price, is what prompted Cohen to finally pull the trigger. And what turned out to be great timing for the Mets wound up blindsiding Vientos, who probably had convinced himself that this spring would be different.

Now he’s got to shake it off.

“That’s the business,” Mendoza said.

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