Ryan Garcia was still TURNT ALL THE WAY UP at his victory party following his KO of Francisco Fonseca ... telling the crowd, "How about that f**king left hook?!"
Just hours after the 21-year-old boxing superstar put together another highlight-reel performance, Garcia and his crew celebrated at a house party in Orange County.
Garcia -- who barely broke a sweat -- grabbed the mic and thanked everybody in the crowd for supporting him in his meteoric rise to boxing stardom ... saying, "This is a team effort."
He also talked about the crazy work ethic that helped him become the WBC silver lightweight champ -- saying, he busts his ass "every f**king day!