After a slow 4,600 metres, 2008 champion Dibaba led an all-African charge but faded in the finishing strait as Defar and Kenya's Cheruiyot overtook her, the winning time 15:04.25.
Defar, who won the gold in Athens eight years ago, reacted with disbelief having been third-best to her podium buddies in recent seasons.
Jo Pavey finished a creditable se
venth, just ahead of British team-mate Julia Bleasdale.
Again the GB pair were the highest-finishing non-Africans in the race, as they were in the 10,000m final earlier in the Games. Meseret Defar wins the women's 5000m in a time of 15.04.25
