By TMZ Sports

Andre Berto got some new ammunition for smack talking Floyd Mayweather Jr., and he's already unloading on him -- blaming the champ for their fight's historically low Showtime pay-per-view numbers for last Saturday's event at the MGM Grand in Las Vegas.

Somewhere between 400,000 and 550,000 people bucked up for the fight ... the lowest PPV stats for a Floyd fight in a decade.

Berto tells TMZ Sports, "It’s definitely Floyd's fault, He left a sour taste in everybody’s mouth because of the Pacquiao bombshell."

Berto thinks Floyd underestimates how much fans hate his style of boxing, and that's why they vowed to stop buying his fights.

"As you can see they weren’t bulls**ttin."

Ultimately the low PPV numbers hurt Floyd more than Berto, since Floyd gets a cut of that. Berto got a flat $4 million purse, but says he still tried to put on a good show ... unlike Floyd.

"I knew if he had the chance he would run around and make it boring, but I tried my best to not let that happen and disappoint the people. They deserve excitement.”