Jamaica’s Britany Anderson took silver in 12.23sec, while Olympic champion Jasmine Camacho-Quinn of Puerto Rico claimed bronze in 12.23.
Amusan had produced a jaw-dropping world record in the semi-finals, smashing the previous best mark of 12.20secs held by Keni Harrison of the United States since 2016.
“Honestly, I believe in my abilities but I was not expecting a world record at these championships,” Amusan said after her final victory. “The goal is always just to execute well and get the win. So the world record is a bonus. I knew I had it in me but I could not believe it when I saw it on the screen after the semis.
“Before the final, I just tried to stay calm and to do my best. I took a deep breath knowing that I have some goal to accomplish and it worked pretty good. I knew it was very fast but not this fast.”
Harrison had been left in Amusan’s slipstream in the semi, and was again shown a clean pair of heels by the Nigerian in the final.
Amusan got off to a scorching start and was smoothly into her stride after the first hurdle, building a clear lead and then pulling away ahead of Anderson and the fast-closing Camacho-Quinn.