FORT MYERS, Fla. — The truth as told by former Boston Red Sox third baseman Tim Naehring to Aaron Boone 15 years ago is as true for Boone – and Alex Cora – today as it was then.

Cora and Boone have no idea what they’re walking into.

We’re not talking about handling their jobs and how they’ll do as first-year managers for big-market, big-expectations teams.

No, this is about the pair being thrust from a brand-new position into the vortex of vitriol, passion, irrationality and resentment known as the Red Sox-Yankees rivalry.

Playing in it is one thing.

Managing in it is another, as Cora and Boone will find out 19 times beginning April 10.

Until then, the two don’t know what they don’t know.

“I was surprised at how big (the rivalry was), said Boone before Saturday’s soft opening for the rivalry, when his Yankees beat the Red Sox, 5-3, at JetBlue Park.

Boone was speaking about what it was like when he first played a game for the Yankees against the Red Sox in August 2003 after being dealt to New York by the Cincinnati Reds at the trade deadline.

“When I think of things that surprise me in the game, in my career or whatever, that’s one of those that sticks out to me – wow, here I thought I knew what was going on in the game and the league, and obviously coming from the National League at that time, so not really experiencing it,” he said. “Tim Naehring was right.”

What Naehring was right about was what he told Boone and his friends in the clubhouse in Cincinnati the evening of July 31, 2003. Naehring was working in baseball operations for the Reds at the time.

“Timmy Naehring was sitting with us,” said Boone. “And he said, ‘You have no idea what you’re walking into now.’ I considered myself a pretty good fan of the game, pretty good knowledge of what the heck is going on. And sure enough, he was right. I remember my first trip into Boston sometime in August, and it was another level, but so much fun.”

Boone, of course, went on to Sharpie his name in Red Sox-Yankees lore with his 2003 ALCS-winning, 11th-inning home run off Tim Wakefield. He was out of pinstripes the next season, winding up with six regular-season games played against the Red Sox.

Naehring went on to join the Yankees, first as a scout before rising through the ranks to become vice president of baseball operations. His current position led Naehring to JetBlue Park on Saturday.

The messenger and the message haven’t changed.

“It’s a different environment – Red Sox-Yankees. People live it and breath it,” Naehring said. “I was watching a Yankees-Red Sox game (Boone was broadcasting) probably five years ago on ESPN, I’m just laying on the couch, and sure enough, he brings up that story on the air. I’m like, ‘Yeah, I remember that conversation.’ That’s what it was – it’s dynamic, it’s unlike anything I ever experienced before. … Obviously, both clubs look like they’re going to be pretty strong, (so) I would imagine the rivalry would be hot and heavy this year. It’s good for the game of baseball.”

Cora, who played in 34 games against the Yankees during his Red Sox stint between 2005-08, gained an inkling of what’s in store in a playoff series last October as bench coach against both the Red Sox and Yankees for the World Series champion Houston Astros.

“It’s a big deal, man, it’s going to be fun, it’s going to be fun,” Cora said. “I was watching Game 4 the other day of the (2017) Division Series, and Fenway was alive in that Division Series, especially in Game 4 after (Rafael) Devers hit that inside-the-park homer, and I was like, ‘This is cool, this is what it’s all about, this is how the fans get into it.’ And Game 3, 4 and 5 of the Championship Series, (Yankee) Stadium was alive. I’m a guy, I go out there 35 minutes before the first pitch, and when I was in the dugout, I was looking around, and the way they were playing and the way their fans were into it, I was like, ‘Oh oh, we’re in trouble.’ Because it had that feeling of the old (stadium). That’s great for baseball.

“The two fan bases, through the offseason, they got what they wanted. One team got it early, the other one did it late, but we are where we are and it should be fun.”

Boone said “maybe I’m delusional,” but he feels as if he’s been treated well by Red Sox fans when encountered on the road or at airports ever since he struck the blow in 2003. Three Red Sox championships since have softened the sting.

Cora and Boone really won’t know what they’re walking into this year until the fans remind them.