The Futures Game, now a staple of Major League Baseball’s All-Star festivities, didn’t exist in 1995. And that’s history’s loss.

We get fired up now for the likes of Michael Conforto (Mets), Aaron Judge (Yankees) and Kyle Schwarber (Cubs), all of whom will play in Sunday’s 17th annual prospects showcase at Cincinnati’s Great American Ball Park. Imagine such an event 20 years ago featuring Baseball America’s top-ranked future star, Alex Rodriguez, and its No. 4, Derek Jeter.

Of course, far from all of Sunday’s participants will attain their full potential, and the game’s poster boy for untapped promise — or wasted talent, as some might put it — would’ve stood alongside A-Rod and Jeter in that hypothetical ’95 game.

As a matter of fact, if you’re not familiar with the tale of Ruben Rivera — No. 2 on that ’95 list, right behind A-Rod and two ahead of his Yankees teammate Jeter — you can go see him in the Mexican League, where, at 41, he plays regularly (and hits pretty well) for the Olmecas de Tabasco.

“I’m still good,” Rivera told The Post, laughing, earlier this week in a telephone interview. “I don’t have injuries. And I love to play ball. I have a good time here. I try to enjoy it, because I love it.”

In MLB, though? Rivera wound up not being very good at all. He’s best remembered for what might have been — and for an ugly off-the-field incident that cast Jeter as a victim.

“He was probably the best five-tool player in the game who never matured to use his talents,” former Yankee Jim Leyritz said. “That’s really all you can say. The guy had every ability there was, but just couldn’t mentally get it together. It was a shame.”

“I really had great hopes for him. He could run, he could throw, he could hit for distance,” said Herb Raybourn, the Yankees’ former director of Latin American operations — who signed Rivera, his better-known cousin Mariano Rivera and their fellow Panamanian Ramiro Mendoza, among others. “He had all the tools. But he also liked to fool around. You have to be serious.”

John Manuel, editor in chief of Baseball America, wrote in an email, “Two of our biggest misses are Yankees — Rivera and [1991 top overall draft pick] Brien Taylor. I wasn’t around for either, but when you research it, we would have been fine on Taylor if he’d stayed healthy. He had incredible talent.

“Rivera … we just whiffed on the makeup, as did the Yankees. Very fair to say he’s a big miss for us.”

As Raybourn recalls it, he already had signed Mariano Rivera, earlier in 1990, when he paid another visit to Panama to look for more players.

“I asked him, ‘Mariano, do you have somebody there?’” Raybourn said. “He said, ‘Yes, my cousin. He can play.’ ”

Raybourn agreed after working out Ruben Rivera. For a $3,500 signing bonus, $1,500 more than his older cousin received, Ruben Rivera became a Yankee in 1990. Just like Jeter, the Yankees’ first-round draft pick in 1992, Rivera made his professional debut with the 1992 Gulf Coast Yankees.

“He was just an incredible athlete, all the way around,” said Wade Taylor, now a Diamondbacks scout, who had pitched for the 1991 Yankees and was rehabilitating his right shoulder in the minors with the 1992 Gulf Coast club. “Physically gifted. Super, super strong. When I saw him, he was really, really, really, really raw.”

That athleticism carried Rivera up the Yankees’ farm system, into the major leagues. He debuted with the big league club in 1995, the same year the Yankees welcomed Jeter, Mariano Rivera, Andy Pettitte and Jorge Posada. There were no known deployments of the term “Core Five,” but Ruben Rivera’s ceiling was just as high as, if not higher than, the others’.

While he spent most of 1996 with Triple-A Columbus, he did join the Yankees for a three-week stint from May 23 to June 14, and he came up for good in late August. He put up a .324/.378/.471 slash line in 38 September plate appearances, helping the Yankees capture their first AL East title since 1978. On Sept. 10 in Detroit, as a defensive replacement in right field for Paul O’Neill, he made a diving catch of Bobby Higginson’s ninth-inning line drive with two runners on base to preserve a one-run lead. On Sept. 18 in The Bronx, he hit a 10th-inning, walkoff single to propel the Yankees over top rival Baltimore.

Even in ’96, though, you could see the warning signs. He complained publicly when the Yankees sent him to Triple-A Columbus in spring training. The team suspended him for seven days in July when he got ejected from a game with Columbus and immediately left the ballpark.

And on Sept. 25, with the Yankees leading Milwaukee, 14-1, in a game that would clinch their division title, Rivera made a pair of impressive, unnecessary throws from right field — one to third base, one to home plate. The Stadium crowd roared with approval, according to The New York Times’ account. However, Rivera aggravated his right shoulder with the throws, and the next spring, he underwent arthroscopic surgery on the shoulder.

He never played for the Yankees again. On April 22, 1997, the Yankees dealt the formerly untouchable Rivera to San Diego as part of a package that eventually sent the highly touted Japanese pitcher Hideki Irabu to New York. In four seasons and 394 games with the Padres, the organization that gave him his best chance, Rivera recorded an underwhelming .204/.301/.397 slash line. San Diego released him in March 2001, and after a year of decent, part-time production (.255/.321/.426 in 117 games) in Cincinnati, the Reds removed him from their 40-man roster.

The Yankees brought him back for 2002, and that chance concluded with a spring-training release when the team determined Rivera had stolen Jeter’s game glove and a bat from the future team captain’s locker, selling them to a memorabilia dealer for $2,500. Rivera confessed to his wrongdoing in a March 13, 2002, interview with The Post’s George King, saying, “I don’t know what I was thinking in the moment, but I brought the glove and bat back to Derek and I apologized.”

This past week, however, Rivera retracted his confession.

“They made up all these stories, and it’s all [bull],” Rivera said. “I didn’t need a glove from [Jeter]. I didn’t need a bat from him. If I asked [Jeter] for a bat, he wouldn’t have given me one. He would have given me five.”

Rivera and Jeter spoke later that season, Rivera said, after he signed with Texas.

“We talked to each other like nothing happened,” he said. “[Jeter] said, ‘I’m not mad at you. I know that nothing happened.’ ”

Jeter’s agent, Casey Close, declined comment for this story.

Upon returning to the Yankees, Rivera said, he received a warning from Mariano Rivera.

“He said, ‘Be careful with some guys in here. Some guys from the organization don’t like you.’ Joe Torre really loved me. Brian Cashman, he’s the guy that didn’t want me there.”

“I think you’d better get Mariano Rivera, because Mariano Rivera’s the one that came to me after meeting with Derek Jeter and said, ‘He’s gotta go,’ ” said Cashman, the Yankees’ longtime general manager. “I would have Ruben check with his cousin about his cousin trying to broker a settlement with his teammate Derek Jeter, and that wasn’t happening. He got voted off the island.”

Mariano Rivera’s agent, Fernando Cuza, who also represented Ruben Rivera during his major league career (but not anymore), declined comment.

“My career came down from that moment,” Ruben Rivera said.

After his Rangers stint in 2002, he played 31 games with the Giants, and that would be his last big league stop. The Yankees actually signed Rivera again in 2005, as he played six games for Single-A Tampa before hurting his right elbow. In 2006, he served a 107-game stint with the White Sox’s Triple-A affiliate in Charlotte.

By that juncture, Rivera had spent some time in the Mexican League, and he made a decision.

“I didn’t want to play in the [affiliated] minor leagues,” he said. “I felt like I could do something in the big leagues. It was kind of hard for me to play in the minor leagues.

“Here in Mexico, they gave me a chance to play. It’s not like the major leagues, but it’s not bad, either.”

So, amazingly, Rivera is a 12th-year Mexican League veteran. Through his first 78 games this season, with two teams, he put up a .300/.381/.481 line in 334 plate appearances.

“He’s still in good shape,” Raul Cano, the Olmecas’ general manager, said in a telephone interview. “He’s in right field, he’s hitting fifth and he’s playing every day so far.”

Last month in Mexico City, a three-day Mexican baseball festival took place at the Zocalo, the city’s central public plaza. More than 150,000 people attended so that youngsters could participate in a Pitch, Hit and Run Clinic organized by MLB, and fans of all ages could watch a Home Run Derby featuring the Mexican League’s top players.

Rivera, invited to compete in the Derby, totaled 27 homers before getting eliminated in the second round. Eight-year major leaguer Jorge Cantu captured the championship.

So you can understand why Rivera doesn’t think much about retirement. To the contrary, he’s ready for another chance for the majors, though he isn’t expecting it.

“I can still run. I can still catch. I can still play center field,” he said. “Now it’s hard for someone to take me because I’m 41. There are a lot of good young players in big leagues.”

He follows the Yankees a little, he said, and roots for them most of all. He spends his offseasons in his native Panama and sees Mariano Rivera there during the former closer’s annual visits.

In all, he speaks like a man with few regrets. Who was happy to discuss his past, his present and his future.

“I try to live my life the right way,” he said. “I want to be a coach [in Mexico].”

It’s not what people forecast for him. Just like the earlier chapters of his career.

Will Sunday’s Futures Game produce similar duds to balance the upcoming stars? Cashman is skeptical.

“I think it’s probably a time in the game when he’s a perfect example: If you only look through the lens of the visual eye, in terms of scouting assessment, he had all the physical tools and was very impressive,” Cashman said of Rivera. “But I guarantee, if you plop him into today’s analytic world and you dissect that player, and you can go back in time with all of today’s stuff, there would’ve been predicted failure. I guarantee it.

“Instead of people being shocked that he flamed out — ‘How did this happen? He was the next Mickey Mantle!’ — in today’s world, that player wouldn’t be packaged as the next Mickey Mantle. That player would be packaged as a lot of swing and miss. Feasting on garbage pitching at the lower levels. And he would’ve had predictable trouble at the higher levels.

“I don’t think there’s going to be misses on players like that, because the league as a whole has higher ground.”

Nevertheless, even in 2015, far from every future star will live up to his hype. Part of the fun for observers is wondering who will boom and who will bust. Leave it to the flamboyant Rivera to stand out as a bust whose likes we might never see again.