UFC's Conor McGregor -- HITS THE CLUB ... Even Harder Than He Hit Chad Mendes

To the victor, GOES THE WHISKEY!!!

UFC badass Conor McGregor PARTIED HIS IRISH FACE OFF in Vegas last night ... celebrating his huge win over Chad Mendes at UFC 189 with a rager at Foxtail in the SLS Hotel.

Didn't matter that his eye was busted open from one of the shots, Mendes delivered in the fight, McGregor used the booze to kill ... partying with scores of Irish fans ... and ring girl Arianny Celeste.

Irish eyes are smiling ...