Yuka Saso beat Nasa Hataoka in a playoff at Olympic Club to tie the record as the youngest U.S. Women's Open champion ever.
The 19-year-old Filipino began the final round trailing Lexi Thompson by one shot but made two double-bogeys over her first three holes to drop five strokes off the pace.
However, Thompson was unable to hold on to her commanding lead after shooting a 5-over 41 on the back nine to give the rest of the contenders a chance.
Saso birdied two of her final three holes to post 2-over in the final round, good enough to get into a playoff with Japan's Hataoka.
After each player made par on the first two playoff holes, Saso drained a birdie putt to clinch her first major victory and match Inbee Park's record to the day as the youngest U.S. Women's Open champion.
Saso also becomes the first golfer from the Philippines to win a major championship.