Floyd Mayweather decided to try his luck at a high stakes video poker machine Sunday night ... and hit a $100,000 jackpot.

For real.

Floyd started off with $20,000 in a "Ten Play Draw Poker" machine -- playing $25 per hand.

Then, as fate would have it ... he hit a Royal Flush on one of his 10 hands ... which paid off a cool $100,000.

He also hit some winners on the other hands he was playing at the time, which paid out an additional $1,250 ... for a grand total of $101,250.