Floyd Mayweather Jr. to fight Andre Berto on Sept. 12

Floyd Mayweather Jr.’s attempt to match late heavyweight champion Rocky Marciano’s 49-0 record at retirement will come against former welterweight world champion Andre Berto Sept. 12 at MGM Grand in Las Vegas.

“I’m ready to get back in the ring on September 12 and prove again to the whole world why I’m ‘The Best Ever,’” said Mayweather. “I always bring my A-game and this fight against Andre Berto is no exception. He’s a young, strong fighter who is hungry to take down the best. Forty-eight have tried before and on September 12, I’m going to make it 49.”

Mayweather (48-0, 26 knockouts) announced on social media Tuesday that he’ll fight Berto (30-3, 23 KOs) on Showtime pay-per-view.

“September 12, 2015 number 49. Come be part of the history. Book your hotel and flights now,” Mayweather tweeted Tuesday morning.

Many fans have expressed little appetite for a bout in which Mayweather will be heavily favored, and the 38-year-old champion recognized that while originally trying to place the fight on CBS.

Creating sufficient advertising revenue in a limited window made it impossible to financially support the endeavor, however. Mayweather has made more than $30 million in each of his prior five Showtime pay-per-view fights.

This bout will be the final one in his Showtime deal. While Mayweather has said he’ll retire after the bout, many expect him to be swayed to return for a 50th fight in May when Las Vegas opens its new arena.

He’s not hurting for money. Mayweather’s unanimous-decision victory over Manny Pacquiao on May 2 generated a record $400 million in pay-per-view sales and Mayweather pocketed in excess of $220 million.

While there were calls for Mayweather to meet someone more challenging on pay-per-view, the champion chafed at repeated criticism aimed at him by former junior-welterweight Amir Khan (31-3, 19 KOs) in news reports, and unbeaten contender Keith Thurman suffered a hand injury in his most recent bout that left him unavailable.

So Berto remains the choice.

“Best believe that I plan to bring it to Floyd and I’m not concerned about what 48 other fighters have been unable to do,” said Berto. “Somebody is getting knocked out and it won’t be me. You don’t want to miss this.”

Florida’s Berto, a native of Haiti, overcame a career-threatening shoulder injury to defeat Riverside’s Josesito by sixth-round technical knockout in March in Ontario.

“I’m happy to be in the running for this fight and am definitely up for the challenge,” Berto said in a prepared statement emailed to reporters last month. “I know it will be a great fight if it happens.”

Despite reports that CBS/Showtime is obligated to pay Mayweather $30 million-plus, that’s a “myth,” one boxing official familiar with the deal said.

Regardless, Mayweather is a powerful draw.

His victories over Saul “Canelo” Alvarez and Oscar De La Hoya rank second and third on the list of richest fights ever.

The card will include a super-middleweight title defense by Badou Jack against mandatory challenger George Groves.

World Boxing Organization super-featherweight champion Roman Martinez of Puerto Rico will also defend his belt in a rematch of his unanimous-decision victory over Mexico’s Orlando Salido.

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Follow Lance Pugmire on Twitter @latimespugmire