PORT ST. LUCIE — The most exciting prospects of the Mets’ spring training have been Ronnie Mauricio, Brett Baty and Mark Vientos, all showing off bats with high ceilings.

The club’s No. 1 prospect, though, has been developing his glove largely behind the scenes.

Francisco Alvarez, after undergoing offseason ankle surgery, has yet to play in back-to-back Grapefruit League games.

He caught a game for just the second time Wednesday, when he partnered with Max Scherzer for a few innings, but the Mets are bringing the slugging catcher along slowly.

The Mets want Alvarez, who has said his ankle feels healthy, to develop as a receiver, and he has been working with two of the best pitch-framers in baseball in Tomas Nido and Omar Narvaez.

The subtle skills are holding back the 21-year-old, but it’s the obvious skills that jump out.

“He’s a very exciting kid and does a lot of things well behind the plate. He’s so explosive offensively and defensively — that’s what I see,” said Glenn Sherlock, the Mets’ catching and strategy coach.

Defensively, Alvarez has an arm that — while it airmailed a throw into center field Wednesday — is nearly as loud as his bat.

In the minors last year, Alvarez experienced the tweaks coming to the majors this season, including the pickoff limits and the larger bases that cut the gap between the bags.

With Triple-A Syracuse, Alvarez threw out 15 of 40 (38 percent) would-be base stealers.

If Alvarez were to match that success in MLB — where 75.4 percent of stolen-base attempts were successful last season — he would become an immediate weapon.

“It’s a plus arm. He can really throw. He comes out of the chute — everything he does is explosive,” said Sherlock, himself a former catcher. “He swings the bat hard. He throws hard.”

Through the early days of camp, there has not been a ton to evaluate from Alvarez, who is 1-for-11 with a walk and five strikeouts in Grapefruit League play.

There are fewer concerns about his bat coming around after 27 Double-A and Triple-A home runs last season before he briefly touched the majors.

But the Mets, who continue to view him as a catcher rather than a designated hitter, want to see how he works with pitchers, particularly ones like Scherzer.

“We talked about how we were sequencing, how we were working together, rhythm, different things we’re seeing,” Scherzer said after throwing three-plus innings to Alvarez against Team Nicaragua. “He did a good job.”

Alvarez, who also last year briefly caught Scherzer — a legend with a deep arsenal and a demanding nature — passed the test.

“When I’m able to catch a person that’s on that level, a Hall of Famer in my opinion,” Alvarez said through interpreter Alan Suriel, “it gives me the confidence that I can catch any other pitcher.”

Manager Buck Showalter called Alvarez, who is outgoing and talkative, “very engaging” and praised his “want to.”

A desire to be the best — and a legitimate major league catcher — is not a problem.

As the Mets develop Alvarez’s softer skills, there is wonder how much they will be needed down the road.

An automatic, electronic strike zone will be used at Triple-A this season as MLB evaluates whether robo-umps eventually will invade the majors, which would eliminate the concept of pitch-framing.

Already, there is a lesser need for Alvarez to master calling games.

If Scherzer wanted to call every pitch Wednesday, his PitchCom would have allowed him.

“It’ll just eliminate a lot of a lot of shaking,” said Sherlock, who added that the pitch clock has made the implementation of the PitchCom — with instant communication — all the more important for catchers.

Alvarez will not break camp with the Mets, but he will try to return to the majors soon.

He listed his goals this season as 1) being healthy and 2) for the team to win as much as it can.

“He has all the skills to be a good catcher,” Sherlock said. “We’re just kind of gradually getting him back into it and building up his playing time, but he’s doing very well.”