Floyd Mayweather -- Blows Off ESPY After-Parties ... Hits Boxing Gym Instead

There were no ESPY after-parties for Floyd Mayweather last night -- just sweat and Gatorade -- 'cause the champ went straight from the awards show to the boxing gym ... and we got the footage.

Sources close to Floyd tell us ... Mayweather has his game face on when it comes to his upcoming fight against Marcos Maidana ... and knows there's no time to screw around.

So, instead of the nightclubs or the private mansion parties, Floyd hit up Ten Goose Boxing Gym in Van Nuys, CA -- where he worked out for nearly 3 HOURS.