Mayweather vs Pacquiao -- Honey, I Shrunk The Fight

Floyd Mayweather vs. Manny Pacquiao is the main event but even the under, under ... UNDER card has some big names -- in the little boxing world, anyway.

"Mini Pretty Boy Money" and "Mini Pacman" went at it in the MGM Grand lobby on Monday ... not far from the full-size ring the resort is using to promote Saturday's huge bout.

You gotta see the stare down between the fighters -- absolutely menacing ... said no one.

But get this ... the ultra flyweights will really fight on Saturday night at Beacher's Madhouse and tickets ain't cheap. For $1500 you get to see Floyd and Manny on closed circuit, and then after that ... Mini Money and Mini Pac will go at it live.