Korir timed 1min 43.71sec, with Algerian Djamel Sedjati taking silver in 1:44.14 and Canada's Marco Arop claiming bronze (1:44.28).
A second Algerian, African champion Slimane Moula, raced into lead of the eight-man field at Hayward Field.
Arop slid through on the inside lane and led through the bell for the final lap.
But at 200 metres, Korir kicked, effortlessly pulling past the field and into pole, holding his nerve down the home straight through to the line for what seemed like an academic victory.
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