Boxer Andre Berto -- CHICK FIGHT AT BDAY PARTY ... 'That S**t Was Nuts!'

Two hot, young chicks strapped on boxing gloves ... in bikinis ... and went at it INSIDE a Miami nightclub to celebrate Andre Berto's 31st bday ... and TMZ Sports has the footage.

The 2-time welterweight champ turnt all way up Mokia Lounge in Miami Beach recently -- alongside big stars like MLB pitcher Aroldis Chapman and fellow boxer Adrien Broner.

The scene was crazy ... huge bottle of champagne, scantily clad women, fancy cake -- and Berto tells TMZ Sports the whole thing was "epic!"

"We partied all night! That s**t was nuts!"

Happy bday!