Justin Bieber -- Flies Posse to Vegas ... All About Floyd "Money" Mayweather

Justin Bieber just high tailed it to Las Vegas with his crew to walk Floyd Mayweather into the ring tonight ... and they're clearly expecting "Money" to kick ass.

Justin boarded with Lil Twist, Lil Za and a few others Saturday for Floyd's fight against Saul "Canello" Alvarez -- and most of his entourage were proudly sporting Mayweather's Money Team shirts.

Worth noting ... no visible puffs of smoke as they boarded the plane ... this time.

8:20 PM PT -- Bieber is officially backstage with the champ.