Harigae set the tone early by making crucial putts to halve the first two holes, then raced out to a big lead and spent the rest of the day holding off Fleet with excellent putting.
She drained an 8-foot putt to halve the first one and a 12-footer on the second.
'When those putts went in, I said 'OK, I can make any putt today,'' Harigae said. 'I just tried to keep my lead. I didn't want to lose it but I knew if I kept trying to make birdies, but not be too aggressive, I'd be all right.'
Harigae, who won the California Women's Amateur as an 11-year-old, then three more times before she was 15, had never made a final in 13 USGA national championships.
'It means so much to me,' Harigae said. 'I worked so hard to get here and now it's paid off.'
Fleet, a junior at Eastern Michigan, was competing in her first USGA championship. She had to win a playoff in sectional qualifying to make this championship and didn't even expect to reach the final.
'But it definitely helps my confidence,' she said. 'I never knew I could compete against the best players in the country.'
Harigae made seven birdies and just one bogey in the morning round and ended with a 5-up lead at the 6,094-yard Kearney Hill Golf Links.
Fleet birdied the 19th and 20th holes of the match, but Harigae made a 10-foot putt to halve the 20th.
With six holes to go, Fleet was down six, but won the next two to stay in the match.
'I told myself to keep playing,' Fleet said, 'keep trying to hit the best shot I could. I didn't have anything to lose.'
Harigae is the fifth high-school-age player to win the Public Links since 2000. Before then, no competitors under the age of 18 had won this championship.
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