Andre Berto -- Pay Attention, Floyd Mayweather Jr. ... I'll Teach YOU About 'History'

Let the trash talk begin -- Floyd Mayweather Jr.'s already counting on Andre Berto becoming his 49th victim, guaranteeing a victory, but Berto says he's about to teach the champ a history lesson.

Money called out Berto on IG, 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, AB 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!"