"He picked the wrong guy," Shepherd, a five-time world champion kickboxer, told the Post.
Shepherd has fought professionally since 1975. He laced into the attacker, throwing a right cross and then a right hook, sending the mugger crumpling.
“I felt (his ribs) crack,” Shepherd said.
Bystanders saw the, melee, and thinking it was a street brawl, intervened, allowing the attacker to run away during the confusion.
Investigators are searching for the suspect. He is believed to be homeless and in his early 20s with long, dark hair.
Shepherd suffered a ruptured eardrum and a cut around his left eye, the Post reported.
He hopes the injuries will not hinder him. In March, he plans to become the oldest person to be in a professional fight.