Spurs' Patty Mills Called 'Jamaican Dog' by Racist Cavs Fan, Responds Like a Boss (UPDATE)

2:00 PM PT -- The Cavs have announced an investigation into identifying the fan behind the comment. As for the phrase, there are discrepancies with what has been reported and whether the fan said "Jamaica called."

“Hey, Jamaican dog -- they want their bobsledder back! Jamaica just called, they want their bobsledder back!”

That was the racist heckling directed at Spurs baller Patty Mills Sunday at The Q ... while he was at the free-throw line at the end of a blowout win over the Cleveland Cavs.

Patty -- who's not Jamaican, but Aboriginal Australian -- didn't hear the taunts during the game ... but when a fan brought it to his attention aftewards, he reacted like a true pro.

"I am a proud Islander. Like my Jamaican Brothers, me & my family in the islands of the Torres Strait have experienced racial slurs for decades. Hope your efforts will enlighten this confused, hateful fan. #BlackHistoryMonth," Mills said.

FYI, this is the second instance of racist heckling in a major U.S. sports league this month. A group of Chicago Blackhawks fans chanted "basketball" at black NHL player Devante Smith-Pelly last weekend ... and were later slapped with a lifetime ban.