The previously unheralded Nawal El Jack secured a gold medal for Sudan with 51.19, breaking the championship record she set in the semi-final.
The 16-year-old, who started the competition with a best of 52.8, ran a steady first 100m out of lane six before turning on the power in the back straight.
Croatia’s Danijela Grgic, in lane four, started to come back at her after 200m but El Jack hung on.
Grgic was second with 51.30 and Cuba’s Aymee Martinez was third with 52.04, both also setting personal bests.
El Jack had improved her best to 52.22 in the heat and was the fastest qualifier for the final with her record mark of 51.83.
