Mets new first baseman Jorge Polanco during a spring training workout...

Mets new first baseman Jorge Polanco during a spring training workout on Thrusday in Port St. Lucie, Fla. Credit: Newsday/Alejandra Villa Loarca

PORT ST. LUCIE, Fla.

Jorge Polanco’s first-base experience over his 12-year career spans exactly one pitch.

The signature moment was April 6 of last season, at San Francisco’s Oracle Park, after Victor Robles fractured his left shoulder crashing into the netting for a highlight-reel catch.

Polanco had the day off, but in the series of ninth-inning defensive moves that followed Robles’ departure, the Mariners suddenly needed a first baseman.

He needed a glove.

“I took Donovan Solano’s glove and went to play first base,” Polanco told Newsday, smiling. “Try to get someone out. They always say the ball will find you, so I was ready.”

On this occasion, it didn’t. Instead, Wilmer Flores punched Gregory Santos’ very next pitch into centerfield for a walk-off single. Polanco’s first-base gig was over in a blink. He barely dug his cleats into the dirt.

Fast forward to Thursday at Clover Park, where Polanco is now the $40 million replacement to former homegrown hero Pete Alonso, and he’s again wearing an unfamiliar glove — a white, miniaturized training mitt. The undersized glove is part of a fielding drill that involves Polanco on his knees attempting to handle grounders at point-blank range.

He’s doing an admirable job, in what looks like a hockey goalie deflecting slap shots, but this is only the warm-up. Next, after shifting over to the actual first-base position, there’s a coach smacking fungoes at Polanco as he advances another step closer with each swing. When that’s over, mercifully, it’s time for the regular infield drills, at the usual distances — flips to the bag, throws to second on the pivot (two scenarios that often gave the Polar Bear problems).

Polanco, at age 32, still has the athleticism and skills to handle the physical rigors of a corner infield spot. He’s logged plenty of games at the other three positions, and first base is the least demanding of those.

The trick is now using the next six weeks to create the muscle memory that convinces Polanco’s mind he’s now a first baseman. And that’s going to mean optimizing every single minute of these workouts, with new bench coach (and defensive guru) Kai Correa as his tutor.

Correa breaks down the learning process into two categories, the “technical” side and the “tactical.” With over 900 career games as a middle infielder, including 410 at second base, Polanco is “really strong” at the former.

It’s the latter part that Correa needs to attack with Polanco, a process that’s well underway.

“The tactical component is what we’re trying to hack into, which he’s really invested in,” Correa told Newsday. “And that’s about exposing yourself to all the responsibilities and scenarios that happen. Where do I go? Where do I rotate to? When do I leave the bag? When do I stretch? When do I jump and tag?

“Oftentimes, in higher levels of baseball, when you see a physical mistake, that’s a manifestation of something mental. Something surprised you. Something caught you off guard. These are the best players in the world, so it takes something like that to throw them off their game.”

Polanco already looks committed to shrinking that margin of error as low as possible. On Thursday, not only did he take live BP against Clay Holmes and Freddy Peralta — that’s no picnic this early in spring — Polanco also grabbed his glove and headed to first base while others were at the plate, trying to get a read on live-action contact. That’s not something veterans typically do during this drill. In fact, Polanco was the only fielder out there.

“This is the perfect time,” Polanco said. “Better for me to get used to the position and make the mistakes that I’m going to make now, in practice, so when it comes time for the games, I’m more prepared. It’s going to be busy for me, but that’s what we’re here for. I want to get ready so I can be there for my teammates.”

Signing Polanco took some outside-the-box thinking by president of baseball ops David Stearns, who was publicly throttled for letting Alonso walk (without as much as an offer) and then replaced him a week later with someone who essentially never played first base. It was almost like Stearns was trolling Metsville with the Polanco move, but there was a method to his perceived madness.

The switch-hitting Polanco was coming off his best performance in a half-decade, batting .265 with 26 homers and an .821 OPS while also cutting his strikeout percentage to 15.6% — down from 29.2% the previous season, the biggest year-to-year reduction in history (according to MLB.com). For comparison’s sake, Alonso was at 22.8% last year.

Polanco credits staying back more, and letting the ball get deeper, for his lower K rate and improved contact. Also, his lower half was much sturdier, thanks to surgery to the patellar tendon in his left knee the previous October. With a stronger back leg, Polanco raked at a .305 clip from the left side, with an .888 OPS.

“The healthier you feel, the more confident you get,” Polanco said. “If you’re hurting, it’s always in the back of your mind. But if you’re healthy, you’re going to be good — even if we struggle at times. You’re just thinking about baseball.”

The Mets now have Polanco concentrating on first base, but the experiment won’t be a success, ironically, until he’s able to stop thinking about it. Once the position becomes second nature to Polanco, Stearns’ Polar Bear gambit won’t feel like such a risk anymore. He’s a long way from a finished project, but they’re working on it.

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