Ryan Garcia Rages at Victory Party, 'How About that F'ing Left Hook?!'

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!"

Garcia is 20-0 with 17 knockouts ... and his last 2 fights have lasted a grand total of 2 minutes and 58 seconds!

So, what's next for Garcia? His promoter, Oscar De La Hoya, says he's already reserved the Staples Center for a fight with former world champion Jorge Linares.

After that ... Garcia has said he wants everyone from Gervonta "Tank" Davis to Devin Haney.