Tausaga is of Samoan heritage and was born in Hawaii.
Tausaga, who finished last in the previous two world finals, came into the showdown with a best of 65.46 metres but found 69.49 with her fifth throw, before sprinting into the crowd to celebrate with her supporters.
Olympic champion Allman owned the top six throws of the season, the best of them almost three metres better than anyone else in the field.
Tausaga said afterwards she doesn't know if she has a fairy godmother or her ancestors had some say in her surprise success.
Ancestors assisting
