Matt Serra says his SHOCKING TKO of Georges St. Pierre at UFC 69 in '07 was the real life version of a Rocky movie -- ONLY BETTER ... 'cause he knocked GSP's ass out!
Serra -- who's gonna be inducted in the UFC Hall of Fame in July -- talked to TMZ Sports about his iconic win ... one most UFC fans consider the most stunning upset in the history of the sport.
In case you forgot ... Serra -- a heavy underdog -- unleashed a fury of punches on the then-welterweight champ .