Gebrselassie clocked an official time of two hours three minutes 59 seconds to beat the time of 2:04:26 he set in Berlin 12 months ago, when he took the world record from Paul Tergat.
Wearing his distinctive yellow vest and yellow shoes, the 35-year-old was inside the required pace from the start and at the halfway stage already 25 seconds faster than his split time last year.
Gebrselassie, who opted not to run the marathon at last month's Beijing Olympics because of concerns about the pollution, dropped the last of his challengers with around six kilometres left and his victory was never in doubt.