The 26-year-old 'Bad Romance' singer is currently in Brazil for her 'Born This Way Ball' tour and surprised kids in the Cantalgo slum when she joined them for a kick-about.
The star, who debuted her new bright pink hair, posted a picture of her hugging young fans on her website Little Monsters along with the caption "wonderful".
Taking to Twitter after the game, GaGa said: "Today was the best day I've ever had, had so much fun.I'll never forget Rio, you lit my heart into flames.
"We even played football, they were SO GOOD IT WAS CRAZY."
Lady GaGa recently donated $1million to the Hurricane Sandy relief effort.