The 23-year-old was left as the ovewhelming favourite for the race after team mate Tirunesh Dibaba decided to skip the 5,000 metres because of illness following her 10,000 metres triumph.
Biding her time in the humid conditions, Defar toook the lead on the penultimate lap and kicked on the final run down the back straight to leave the field for dead, crossing the line in 14 minutes 57.91
Vivian Cheruyiot of Kenya was second in 14.58.50 with her fellow Kenyan Priscah Jepleting Cherono pipping a third compatriot, Sylvia Jebiwott Kibet, at the line for bronze in 14.59.21.
Photograph: REUTERS/Dylan Martinez