Mark Vientos, left, and Brett Baty at Amazin' Day at...

Mark Vientos, left, and Brett Baty at Amazin' Day at Cit Field on Saturday. Credit: Jeff Bachner

Brett Baty overnighted a first baseman’s glove a few weeks ago. Mark Vientos has been taking reps at the position. Carlos Mendoza threw out names such as Jared Young and Joey Meneses as possibilities on Saturday at the Mets’ Amazin’ Day.

And owner Steve Cohen said it flat-out: Unless something drastic changes in the Pete Alonso negotiations, the Mets will use internal options to fill the polar bear-size hole in their infield.

Saying he thinks the Mets might have to move on without Alonso, Cohen said, “I don’t like what’s been presented to us [in Alonso’s contract negotiations].”

Added president of baseball operations David Stearns: “We also feel really good about the young players that are coming through our system that have the ability to play.”

For what it’s worth, Stearns and Cohen were peppered by chants of “bring back Pete!” Those comments by Stearns were greeted by a sea of boos.

But the reality of the situation remains: Baty, who hasn’t played first base since his sophomore year of high school, and Vientos, a third baseman, currently are the Mets’ best options at the position, and that might not change by the time pitchers and catchers report on Feb. 12.

It’ll be a steep learning curve, though both have prepared for the possibility for a few weeks. Incidentally, that’s the same span during which talks with Alonso seemed to significantly stall.

The Mets on Saturday held Amazin' Day at Citi Field with about 10,000 fans and various players in attendance, but the attention of many was on the absence of unsigned fan-favorite Pete Alonso. Newsday Sports' Laura Albanese reports. Credit: Ed Quinn; Photo Credit: Jim McIsaac

“I love playing third base, but right now, my main focus is doing what I can to help us to get to the World Series and win a championship,” Vientos said. “I’m pretty comfortable [at first]. I’ve played there the last couple of years and I’ve gotten a couple of reps there.

“I’ve just been working on some footwork stuff around the bag and some picks, and I should be good ... I started maybe a week or two ago and just footwork around the bag is the main thing, because I’ve taken millions of ground balls around first base. It’s the same thing. It’s more so the footwork around the bag and the picks and just kind of getting familiar with different plays that could happen and just visualizing different plays and different scenarios.”

Mendoza said the situation at third base is still fluid, and he expects a competition come spring training: It could be Vientos, Ronny Mauricio or Baty. Luisangel Acuna, a natural shortstop who also plays second, also has started taking reps at third.

Baty said Stearns called him about two weeks ago and told him to start looking toward first. Baty, who spent most of last season in the minors, hung up and immediately ordered his new glove.

“It’s still pretty new to me and I’m still trying to figure it out, but I think it’s the footwork on the bag,” Baty — one of the more than 50 players, alumni and executives on hand for the event, which attracted more than 10,000 fans — said Saturday. “I think the ground balls are going to come simple, just like third base or second base. I think it’s going to be the footwork just receiving throws .  .  .

“I have an infield trainer back home and he works with a variety of different infielders. He’s been teaching me the tricks of the trade and stuff like that, and I’ve also been watching video. He’s been watching video, I’ve been watching video just on drills and stuff where I can get better.”

Picking it up has been “really fun,” Baty said. “I’ve always prided myself on being as athletic as I can, and I think with athleticism, you can show it off at any position, whether it be first base, second base, the outfield, third base, wherever it is.”

But even so, no one has forgotten Alonso. Not the fans, not his manager and not his teammates.

“I would love to see Pete back with us,” Brandon Nimmo said. “But I understand that I don’t make those decisions. That’s between Pete and our front office and Dave and Steve.”

It sure is. And for now, it seems as if those decisions are leading to a breakup.

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