Mayweather vs. Berto -- Showtime Sues ... It's Our Fight, Not Yours!!!

Floyd Mayweather and Andre Berto just got owned ... by Showtime, which is now gunning for anyone who tries to lure viewers away from the pay-per-view channel.

Showtime is suing a bunch of websites that have declared their intention to livestream Saturday's fight at MGM Grand in Vegas.

The company is asking a judge for an order blocking the sites from doing the dirty deed.

Showtime has a lot to deal with ... thousands of tickets have gone unsold and there seems to be a universal lack of interest in the fight.