His Yankees had just won three championships in four years, and George Steinbrenner could not have cared less. His team was about to play the Mets in the 2000 World Series, and Steinbrenner made sure general manager Brian Cashman understood the terms of engagement.

“You’d better win,” the owner said. “Or else.”

Cashman and manager Joe Torre were positively terrified of what the Mets represented in their employer’s mind. As much as Steinbrenner hated losing, he hated being embarrassed even more. And nothing was more embarrassing to The Boss than getting beaten by the city’s lesser baseball tenant.

In his definitive book on the Yanks’ longtime ruling family, “The Bosses of the Bronx,” Mike Vaccaro writes of Steinbrenner responding to a spring training loss to the Mets about 50 years ago by storming into the clubhouse and berating his manager, Billy Martin, who was busy drinking beer with Mickey Mantle.

In the 2000 Subway Series, the only time the Yankees and Mets met for the heavyweight title, naked fear compelled the Yanks to prevail in five games. “I felt like if we lost to the Mets,” Cashman said, “it would’ve diminished our three championships. It would’ve been like they didn’t count.

“I’d never before been scared of losing. But I was scared of losing to the Mets.”

All these years later, with another round of opening days upon us, the Yankees and Mets are still measured against each other first and foremost, from Queens to the Bronx and beyond.

Which roster is better? Which manager is under more scrutiny? Which owner will spend more in an arms race that threatens to wipe out the 2027 season in what would feel like an apocalyptic big-league event?

Mets owner Steve Cohen, whose net worth of $23 billion (according to Forbes) dwarfs that of Hal Steinbrenner’s $1.7 billion, is, on one hand, a potentially lethal threat to Yankee superiority as a hedge-fund titan willing to pay what it takes. On the other hand, Cohen failed to meet his timetable of winning a World Series within his first five years on the job — in fact, he failed to reach the World Series — and presided over a team last year that fell apart, forcing an overhaul and a series of bittersweet goodbyes to veteran fan favorites.

“We haven’t won,” Cohen said. “And I really want to win. Each year that goes by, I get more annoyed.”

Just not as annoyed as his fan base, which hasn’t celebrated a title in four decades.

It’s true that the Mets’ collapse, their roster reconstruction, and their failure to realize Cohen’s dream of becoming Dodgers East qualify them as a club facing intense pressure on the rebound.

But nobody is facing more pressure this season than the Yankees, who open Wednesday night in San Francisco.

Start with the mother of all labor battles on deck, with major-league players swearing they won’t agree to a salary cap that their counterparts have accepted in other leagues. Hard as it might be to believe, owners and players would actually kill off a season in prosperous times before cutting a deal; some baseball people are already preparing for the worst.

More than a handful were around in 1994 when a work stoppage did what world wars and pandemics could not — cancel a World Series. They’ve seen the unthinkable happen.

This nightmare scenario hovers over all of baseball this year, and specifically over the Bronx, where the home team has claimed one championship in the last 25 years and none since 2009. Aaron Judge, all-time great, turns 34 next month.

That ticking clock on Judge’s prime — and on this entire era of Yankee baseball — is louder than ever now, and not merely because the slugger failed to deliver for Team USA in the World Baseball Classic, reheating questions about his big-game performances.

Judge doesn’t deserve to go down as the Babe Ruth of all superstars who have never won a ring, no doubt about that. He plans to play past his 40th birthday and has cited Tom Brady’s ageless success as a pocket passer for what he could be as a DH in the endgame of his career.

But given the captain’s size and the potential for injury, every year needs to be treated as a precious asset. And that’s where his manager comes in.

Aaron Boone has made the playoffs seven times in eight years in a job that doesn’t charge the person holding it to make the playoffs. Boone was hired to win a World Series at some point, like his predecessor, Joe Girardi, did in his second season. This would be a good time to go ahead and do that.

“I’ve been openly willing to challenge anybody that we don’t have a championship-caliber roster and team,” Cashman said in January, when he was already tired of complaints that he was bringing back the same squad that didn’t even reach the ALCS, complaints later notarized by Judge himself.

“Brutal” and “pretty tough to watch” read the captain’s scouting reports on his team’s early inaction in free agency.

“I’m like, ‘Man, we’re the New York Yankees.’”

And that speaks to the essence of where his club stands today. The Yankees are actually no longer the Yankees; the Dodgers, two-time defending champs, have replaced them as baseball’s premier franchise and big-game hunters. Per Spotrac, the Dodgers’ estimated payroll and tax bill stands at an estimated $538 million, or $149 million more than the Yanks’ bill.

Hal Steinbrenner has confronted obstacles that his father didn’t have to deal with, namely Dodgers and Cohen money. But in the end, it’s on the son to figure out a way to make a Boss move back to the top. Nobody said it was going to be easy.

Across town, the Mets have enough of their own problems, which they’ll start to sort out Thursday against Pittsburgh at Citi Field, the first day of another franchise reboot. But even if they fail to regroup and win it all, the Mets don’t carry the same burden of expectation into every season.

They’re not the Yankees. They don’t have the history or the rings or the monuments or the ghosts.

In the movie “Catch Me If You Can,” Christopher Walken’s character asks his son, played by Leonardo DiCaprio, the following question:

“You know why the Yankees always win, Frank?”

“Because they have Mickey Mantle?” DiCaprio’s character replies.

“Nah, it’s ’cause the other teams can’t stop staring at those damn pinstripes.”

Nobody really stares at those pinstripes like they used to. Make no mistake: The 2026 Yankees will be under heavy pressure to change that.

As the late George Steinbrenner might’ve told them, “You’d better win … or else.”