Floyd Mayweather's Dad: My Son Fought Fair ...100%

Floyd Mayweather's famous dad is in his son's corner -- telling TMZ, there was nothing underhanded about Floyd's sucker punch victory on Saturday ... adding, "The fight was 100% fair."

Floyd Mayweather Sr. tells us, "First of all, Ortiz headbutted Floyd and that was obviously intentional. If you re-watch the fight, you can see that right after they apologize to one another, the ref OK's them to fight."

"Floyd did the right thing -- the number one thing they will tell you in fighting is to ALWAYS protect yourself ... The way Floyd ended the fight was 100% fair."

Tell that to angry mobs everywhere.