Aman, the only man to beat world record holder David Rudisha since 2009 and pre-race favourite in the absence of the injured Kenyan, pipped American Nick Symmonds for victory in 1:43.31.
Djibouti's Ayanleh Souleiman was third.
It was Ethiopia's first world gold at a distance below 5,000 metres.
World indoor champion Aman, a disappointing sixth in last year's amazing Olympic final in which Rudisha smashed the world record, found himself boxed on the inside on the final lap but as the pace wound up towards the finish he found space for his late charge.
- Sports & Recreation
- David Rudisha
- Nick Symmonds
- Ayanleh Souleiman