Jameis Winston Parties Like Middle Schooler After Heisman Win -- Just a Coke for Me, Please

Jameis Winston celebrated his Heisman Trophy win by partying it up in NYC Saturday night ... hanging out with fans at a popular FSU bar and popping bottles ... of Coca-Cola, TMZ Sports has learned.

The 19-year-old phenom dropped by the Saloon in NYC at around 12:30 AM after the awards ceremony ... and we're told he balled out with an ice cold coke and a water for his GF.

Sources from the Saloon tell us ... a fan offered to pick up his bill but Jameis declined, and dropped a $20 on a $3 tab.

We're also told ... the QB was hungry but the kitchen was closed, so staff actually ordered him a pepperoni pizza from a nearby pizza joint, which he paid for in full.

Winston took time to pose for pictures with every fan in the bar before continuing on with his sugar-fueled bender.