Keyla McCree squeezed through an air conditioner vent and plummeted around 30 feet – at the split second that bus driver Steven St Bernard was heading home from work.
With lightning-quick reactions he caught the little girl in his arms – and both he and Keyla were virtually unharmed.
Shocked neighbours in Coney Island, New York, US, caught the amazing moment on video at 2 o'clock in the afternoon.
The girl's mother Saleema McCree said: "I heard somebody banging on the door, stating that my daughter was outside on the air conditioner, but I had no idea what was going on because I had my son."
She said the unit was not secure and the side vents easily opened, which allowed her daughter to squeeze through and get out.
"They sold me a defective air conditioner," she said.
Onlookers said that girl started dancing on top of the AC before she plummeted.
Jeremiah Fernandez, 12, said: "I was kind of a little scared, I have never seen anything like that up close before."
Hero Steven St Bernard happened to be walking by and saw the girl seconds before the fall.
"Basically she was dancing and I was just praying that I would get there and that if she [fell] that I would catch her," he said.
"She was shocked, because she moaned a little bit."
Police rushed to the scene, taped off the area and transported the child and Steven to Coney Island Hospital. The young girl didn't suffer any injuries, but Steven suffered a torn tendon in his hand.