The New Zealander cried with joy after winning her third professional title from 12 events at the age of 15 years, eight months and 17 days.
"I didn't cry at the Canadian Open so I don't know why I cried here," Ko said. "I guess it meant more. It is our national open so to win means a lot."
Ko, who made a three-foot putt on the final hole to finish on 206, one ahead of American Amelia Lewis, beat the record set by South Korean Amy Yang, who was aged 16 years, six months and eight days when she won the Ladies Masters in Australia as an amateur in 2006.
Ko became the third amateur to win on the women's European Tour, after Gillian Stewart, at the 1984 European Open, and Yang.
"It means a lot and makes it more special to be the first New Zealander to win the women's Open," the schoolgirl said. "It is always special to make history. I guess I broke history again."
Ko, already number 38 on the world professional rankings, now heads for the Australian Open in Canberra, which starts on Thursday.
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