South Africa's Wayde van Niekerk held off the challenges of LaShawn Merritt and Kirani James to win the world 400m title in an incredible 43.48 seconds.
The 23-year-old overhauled early leader and 2013 champion Merritt in the final 150m and held his form to cross the line with the fourth fastest time ever.
USA's Merritt took silver with 43.65 while Grenada's Olympic champion James was third in 43.78.
Great Britain's Rabah Yousif was sixth in 44.68.
Britain's Eilidh Child was sixth in 54.78 in the 400m hurdles final, while her team-mate Holly Bradshaw finished seventh in a thrilling pole vault final with 4.70m, failing three times at 4.80.