By TMZ Sports

Let the trash talk begin -- Floyd Mayweather Jr.'s already counting on Andre Berto becoming his 49th victim, guaranteeing a victory on September 12th at the MGM Grand in Las Vegas, but Berto says he's about to teach the WBC/WBA welterweight champ a history lesson.

Money called out Berto on the social networks, saying, "September 12, 2015 for number 49. Come be part of the history."

If Floyd wins, he'll tie Rocky Marciano's perfect 49-0 record.

Now, Berto tells TMZ Sports Mayweather's boast "sounds good, but he gonna be in there with a different animal bro."

As for Floyd's undefeated streak continuing ... Berto says, "We focused and dialed in ready to make history!"