Joey Chestnut TASTES DEFEAT -- Out-Eaten In World Gyoza Championships

Joey Chestnut -- perhaps the greatest competitive eater in the history of food -- had a giant helping of DEFEAT at the World Gyoza Eating Championships this weekend ... and TMZ was there for the whole thing.

Chestnut -- the reigning Gyoza eating champion (266 in 2012) -- was chewed up and spit out by 21-year-old eating prodigy Matt Stonie ... the #4-ranked eater on Planet Earth.

It all went down at the Japanese American Cultural and Community Center in L.A. ... where Chestnut stomached 251 gyozas and Stonie threw down 268!!!!

After the competition, Stonie told TMZ he plans to fart a lot this week -- "It's competitive eating. What do you expect?"

As for Chestnut -- who still holds titles in hot dogs and chicken wings -- he said, "I just didn't find my rhythm and Stonie came out hungry."

Never one to lack confidence, Chestnut added -- "I'll be back next year. I'll win it."