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Sofia Vergara celebrated "Modern Family's" big Emmy win last night by shaking her ass like a CHAMPION in a tight sexy dress ... and TMZ has ALL of the incredible jiggly footage.

It all went down at the HBO Emmy Party at the Pacific Design Center -- when Sofia stormed into the place around 1 AM with the urge to dance her face off in her ultra-skin tight dress.

Sofia -- clearly excited her show won the statue for Best Comedy Series-- went straight to the center of the party and began gyrating to Gloria Estefan's "Conga."

With the crowd egging her on, Vergara requested the DJ play the Enrique Iglesias track, "I Like It"... and of course, he obliged.