LAS VEGAS - In what is expected to be the final fight of his illustrious 19-year career, boxing superstar and pound-for-pound king Floyd "Money" Mayweather (48-0, 26 KOs) will put his undefeated record and WBC and WBA Welterweight World Championships on the line against power-punching, two-time welterweight world champion Andre Berto (30-3, 23 KOs) Saturday, Sept. 12 at the MGM Grand Garden Arena in Las Vegas, live on SHOWTIME PPV (8 p.m. ET/5 p.m. PT).

Coming off of the Mayweather vs. Pacquiao event, in which Mayweather remained undefeated by taking a unanimous decision victory, Mayweather will test himself against a hard-hitting fighter hungry for his chance to score a historic upset. Mayweather could also make history. If triumphant, he would match the record of the late heavyweight champion Rocky Marciano, who retired in April 1956 with a record of 49-0. Equaling Marciano's record, one of the most hallowed in all of sports, would reaffirm Mayweather's legendary status in the sport and buttress Mayweather's claim as "The Best Ever."

Roman "Rocky" Martinez (29-2-2, 17 KOs) will risk his WBO Junior Lightweight title in a rematch against the boxer he dethroned, four-time world champion Orlando "Siri" Salido (42-13-2, 29 KOs). Their first fight, in April of this year, is considered by many to be a leading candidate for Fight of the Year. In addition, Badou Jack "The Ripper" (19-1-1, 12 KOs) will make the first defense of his WBC Super Middleweight World title against mandatory challenger "Saint" George Groves (21-2, 16 KOs). A fourth fight on the pay-per-view telecast will be announced soon.

Promoted by Mayweather Promotions, the four-fight pay-per-view telecast will be produced and distributed live by SHOWTIME PPV and is the sixth and final fight of a record-breaking deal between Mayweather and Showtime Networks Inc. SHOWTIME Sports® will support the event with the Sports Emmy® Award-winning series ALL ACCESS.

Ticket pricing and on sale information is forthcoming later this week.

Martinez, 32, of Vega Baja, Puerto Rico, will make the first defense in his third stint as WBO Junior Lightweight World Champion. He won the WBO 130-pound crown the second time with a 12-round split decision over Miguel Beltran Jr. in September 2012. The ultra-tough Martinez made two successful defenses, including a close points' triumph over previously undefeated Diego Magdaleno, before losing by eighth-round knockout to unbeaten Mikey Garcia in November 2013.

The 5-foot-8 Martinez won his first fight following the Garcia bout and then, in his most recent outing, he survived a desperate late rush to unanimously outpoint Salido across 12 hard-fought, action-packed rounds last April 11.

Billed as "The War," the slugfest may have exceeded its billing as both fighters expended an inordinate amount of energy over the course of 36 minutes. Utilizing his advantages in height and reach, Martinez sent Salido to the canvas in the third and fifth and won by the scores of 116-109, 115-110 and 114-111.  Salido was docked a point in the 11th round for a low blow, but never quit fighting and was in it to the end.

Tough and determined with a straight-forward style that makes for crowd-pleasing affairs, Martinez captured the WBO Title the first time in March 2009 and successfully defended it twice.

Salido, 34, of Sonora, Mexico, is a relentless hard-nosed boxer-puncher who is willing to take on anyone and is no stranger to the boxing rivalry that is Mexico vs. Puerto Rico.

The 5-foot-6 Salido captured the interim WBO Junior Lightweight World Championship in his outing before last in a back-and-forth 11th-round knockout over Thailand's Terdsak Kokietgym on September 1, 2014. The brutal battle that featured seven knockdowns (Salido went down three times, Kokietgym four) was the 2014 Yahoo! Sports Fight of the Year.

Salido is also a two-time featherweight world champion. He fought some of the best of his generation at 126, including Mikey Garcia, Juan Manuel "Juanma" Lopez twice, and current WBO 126-pound champion Vasyl Lomachenko who Salido beat three fights ago on a 12-round split decision in March 2014.

Jack, 31, a native of Stockholm, Sweden, who fights out of Mayweather's Las Vegas gym, captured the WBC 168-pound belt with a 12-round majority decision over defending champion and previously unbeaten Anthony Dirrell last April 24 by the scores of 116-114, 115-113 and 114-114.

A former European amateur standout - he's the only boxer ever to represent Gambia in any Olympic Games (2008) - the 6-foot-1 Jack turned pro in June 2009 and won his initial 16 bouts before suffering a shocking first-round knockout loss to Derek Edwards in February 2014.

A boxer with good speed and movement, Jack has since won three in a row, including the major victory over Dirrell.

The battled-tested Groves, 27, of Hammersmith, London, England, will get his third crack at a 168-pound world title. The only blemishes on his record came in back-to-back fights against then-IBF/WBA champion and countryman Carl Froch at Wembley Stadium in London. After losing by controversial ninth-round TKO in November 2013, Groves was stopped by his fierce rival in the eighth round of a May 2014 grudge rematch that attracted 80,000 fans.

Groves has rebounded since falling to Froch, winning his last pair. Groves captured the vacant WBC Silver Super Middleweight title and European Championship in Sept. 2014 against Christophe Rebrasse and scored a seventh-round TKO over Dennis Douglin last Nov. 22.