Casie Cathrea beat defending champion Minjee Lee with a par on the 19th hole Thursday to advance to the US Girls' Junior quarterfinals at Sycamore Hills.
Cathrea, the 17-year-old Livermore, Calif., player who was the low amateur in the US Women's Open, won the par-4 18th with a bogey to extend the match, and finished off the 17-year-old Australian on the par-4 first.
Cathrea's hands trembled as she stood over her 4-foot bogey putt on 18.
''I was like, `OK, calm down,''' said Cathrea, who will attend Oklahoma State. ''Then my caddie was like `It's just a 4-foot putt.' And so I make it, and my hands are still shaking and I'm like, `Breathe, relax, you've got another hole.' ''
Cathrea, a 3-and-1, second-round winner over Jennifer Kupcho of Westminster, Colo., in the morning, will face Bethany Wu of Diamond Bar, Calif., on Friday morning.
''Now I feel like I'm ready to play and I'm going to come out in the morning and play my best,'' Cathrea said.
Lee looked ahead after the loss.
''I'm just going to go win the US Women's Amateur,'' she said.
Wu beat Samantha Wagner of Windermere, Fla., 1 up.
In the other lower-bracket quarterfinal, Lakareber Abe of Angleton, Texas, will meet Kathleen Scavo of Benicia, Calif. Abe beat Lilia Khatu Vu of Fountain Valley, Calif., 2 and 1, and Scavo edged Mai Dechathipat of Oakton, Va., also 2 and 1.
In the upper bracket, Megan Khang of Rockland, Mass., will face Sabrina Bonanno of Norridge, Ill.; and Yueer Feng of Orlando, Fla., will play Gabriella Then of Upland, Calif.
Khang beat Maddie Szeryk of Allen, Texas, 3 and 2; Bonanno topped Mexico's Maria Fassi 5 and 4; Feng beat Australia's Hannah Green 5 and 4; and Then routed Cheyenne Knight of Aledo, Texas, 6 and 4.