World No.1 amateur Lydia Ko has fallen one match short of the US Junior Girls' Amateur Final at the Lake Merced Golf Club in California.
The 15-year-old, who defeated Yueer Feng of Florida 8 and 6 in her quarterfinal match in the morning, was upset by local Alison Lee by 2 and 1 in a tight semifinal.
Lee went one up early with a par to Ko's bogey on the second hole, but the Kiwi made a par and a birdie on six and seven to turn the match around and reach halfway one up.
The Californian won the 10th hole to square the match up and it remained that way until the 15th hole, when Lee clinched the win with a par and then a birdie on 16 to take the ascendancy at a crucial time.
When the American made par on the 17th, she had secured a 2 and 1 win, and Ko's dream of winning the US Junior Girls' Amateur was over.
World No.2 Ariya Jutanugarn of Thailand, who won the two-round qualifying to be top seed, was also upset by Australian Minjee Lee, 2 and 1.
The two Lees will square off in the 36-hole final to decide the title.