Maurina jumped on the beast and used her fingers to block its nose, forcing it to release its grip on the boy.
She managed to snatch Gideon away but the crocodile bit her hand.
Her boy was rushed to hospital after the horror, near Gonarezhou National Park, with severe bleeding and facial injuries that were making it hard for him to breathe.
But he has since made a full recovery.
Maurina, from Chihosi village, Chiredzi, said: “I pressed its nose hard, a tip I learnt from the elders long back.
“If you suffocate a crocodile from its nose it loses its strength and that is exactly what I did.
“I used my other arm to free my baby’s head from its jaws. Even to this day, I still do not believe I rescued my son.”
The reptiles breathe mostly through their mouths but when grappling with prey in the water, the mouth valve stays shut and they breathe through their nostrils.
The Runde River is swarming with Nile crocodiles – which can grow up to 20ft long and weigh up to 120 stone. They are thought to attack more than 200 people a year.