The U.S. singer was to be the surprise closing act for Mandela Sports and Culture Day in Soweto last Saturday, but most of the crowd didn't realize she was to perform and left before she took the stage.
There were no more than 40 people present by the time she arrived, the Guardian newspaper said.
"Brandy performed to an empty stadium. With the stadium lights on," South African musician Kabomo tweeted. "People didn't know there was a concert after the games. No one knew Brandy was around. Maybe a 40 people audience... she sulked after two songs and walked off."
Tens of thousands of people filled the stadium for the day of football and rugby matches, as well as performances by David Jenkins, Elvis Blue, Salif Keita and D'Banj, the New York Daily News said.