PORT ST. LUCIE, Fla. — Tim Tebow got down to business Monday in his first day as a professional baseball player.

And his new employer got down to business, too. The business of selling Tebow.

As the former Heisman Trophy-winning quarterback arrived at the Mets’ spring training complex for the start of Instructional League workouts, the team’s official website began offering Tebow No. 15 jerseys and T-shirts.

The pinstripe jerseys cost $119.99. The blue and orange (or orange and blue, your choice) T-shirts cost $29.99.

By the time Tebow took the field under a broiling sun in front of about 400 fans, 70 media members and a TV news helicopter, his jersey had soared to third on the Mets’ most popular list, just behind Noah Syndergaard and “Your Name Here.”

Vote

Vote: How far will Tim Tebow make it with the Mets?

Class A Class A-Advanced Class AA Class AAA MLB

“I heard that was something that they might be selling,” Tebow said. “What do I think about it? It’s cool.”

advertisement | advertise on newsday

“Your Name Here” may have as good a chance of making the majors as Tebow, who is attempting to start a baseball career at the age of 29 after having last played the sport as a junior in high school in 2005.

Tebow might never reach Citi Field . . . but chances are his merchandise eventually will.

“The goal is to one day play in the bigs,” a relentlessly smiling Tebow said. “I don’t know if there’s a backup goal.”

The Mets signed Tebow on Sept. 8 after attending a showcase workout with 27 other major-league teams. General manager Sandy Alderson denied that the Mets signed Tebow as a marketing move, saying he was intrigued by the former Jet’s baseball abilities.

Those abilities were on display Monday. Tebow stretched with approximately 50 other players — most of whom are much younger than he is — then was grouped with outfield prospects for baserunning drills, batting practice and fielding practice.

Mets videos

It was the batting practice that drew the most attention and applause, although Tebow had been cheered earlier for simply taking a lead off first base and returning safely to the bag.

The 6-3, 255-pound lefthanded hitter showed an ability to loft the ball in four rounds of batting practice against righthander Jose Carreno, the manager of the Gulf Coast League Mets. Tebow hit the centerfield wall twice with drives.

He was asked to autograph a few footballs when the day’s work was done.

“Thankful for people showing up and rooting for you and cheering for you,” Tebow said. “It’s pretty awesome.”

Tebow, who also has an autobiography coming out next month called “Shaken,” is wildly popular in Florida after leading the Gators to two national championships. Several of his fans had purchased and already were wearing Tebow Mets T-shirts, which were on sale along with the jerseys at the entrance to the Tradition Field complex.

advertisement | advertise on newsday

Other fans wore Tebow jerseys from one of his NFL teams, the New England Patriots. The Patriots need a quarterback now with Tom Brady suspended and fill-in starter Jimmy Garoppolo injured, but Tebow slammed the door shut on that thought.

“No, sir,” he said when asked if he would entertain a return to the NFL. “I’m part of the Mets family . . . I have to play baseball now. That’s what I would tell them.”

Tebow also said the Patriots didn’t call.

Tebow will be at the three-week camp from Monday through Friday. He will miss Saturday sessions with the Mets’ blessing as he fulfills his college football broadcasting commitment with the SEC Network. Sunday is a day of rest in the Instructional League.

“This is something I had to do because I gave my word to my SEC family,” Tebow said. “I’m a big believer in that.”

advertisement | advertise on newsday

Tebow also said he is not looking to prove people wrong about his baseball journey. He’s too positive a person for that.

“You always want to prove it,” he said. “Especially to the Mets’ organization and your teammates, Mr. Alderson and everybody that gave me a chance. You want to prove them right. Show them that it was the right decision.”

In one sense, it already is. By the end of the day, Tebow’s jersey was No. 1 with the Mets — and the third-highest seller in all of baseball.