The dramatic birdie putt made Chuasiriporn the leader in the clubhouse for about 15 minutes, until Se Ri Pak parred the last hole to tie the Duke University student and force an 18-hole playoff between the 20-year-olds today at Blackwolf Run Golf Course.
Chuasiriporn, the daughter of Thai immigrants who is entering her senior year at Duke, closed with a 1-over-par 72 over the demanding 6,412-yard course for a 72-hole score of 6-over 290.
Pak, an LPGA Tour rookie from South Korea seeking her second straight major championship, led by 1 stroke entering the round. She struggled with a 40 on the front nine but gathered herself to shoot par on the back for a 76.
While the 72-hole score is the lowest ever posted by an amateur in the Women's Open, it is the highest winning score at an Open since Jan Stephenson shot 6-over 290 to win the 1983 championship at Cedar Ridge in Tulsa, Okla.
Liselotte Neumann of Sweden hurt her chances to contend with poor putting and wound up 1 shot out of the playoff at 291 after a 76. Danielle Ammaccapane mounted a charge with a 71 and tied Pat Hurst (73) and Chris Johnson (74) for third at 292.
Mhairi McKay, a tour rookie from Scotland who started the day 1 shot behind Pak, tripled-bogeyed the seventh hole in a round of 78 and fell to a three-way tie for sixth.
The wind died down a bit from Saturday, but Blackwolf Run still had plenty of teeth with tough rough and hard greens. Only one player, Lorie Kane, broke par. The veteran names on the leader board - Neumann, Hurst, Johnson, Dottie Pepper and Laura Davies - were unable to mount a rally.
But as for the two kids who have yet to reach legal drinking age, there was no problem. Chuasiriporn felt all week as if she had nothing to lose. Pak, the winner of the McDonald's LPGA Championship in May, rarely showed any nerves.
``That is hard to explain,'' Chuasiriporn said. ``I can only speak for myself, but I really just tried to hit a lot of fairways and greens. I didn't have too many expectations.''
Chuasiriporn began the day 4 shots behind Pak, but rallied and held or shared the lead from the time she birdied the par-3 eighth hole to her bogey at No. 15. When she got to the tee at the 421-yard 18th hole, she trailed Pak, who was just about to tee off at the 17th, by 2 strokes.
Playing in the twosome in front of Pak, Chuasiriporn hit a drive and an 8-iron into 18, with the ball winding up 45 feet past the hole. While she lined up her putt, Pak was making bogey behind her, missing a 10-foot par putt, and the lead dropped to 1.
Team Chuasiriporn - Joey plays for Penn State - worked together lining up the birdie putt. Joey took care of the break, Jenny the speed.
``He said to hit it about a foot left,'' she said. ``I didn't want to think about the break because I was trying to feel the putt. I hit it the way I wanted to. I didn't expect it to go in at all. I was really thinking 2-putt from there.''
Two-putt? No. One-putt. Yes!
``It was so overwhelming after it went in,'' she said. ``I turned to my brother, and he was almost in tears, so we really couldn't think straight at that point.''
Meanwhile, Pak split the 18th fairway with her tee shot and knocked her approach to 10 feet. With Chuasiriporn watching, Pak's chance to win ended when the putt curled off to the low side, followed by a tap-in par for the playoff.
``Maybe she can win, maybe I can win,'' Pak said. ``I will do my best, the same way I played this week, the same thinking. [The playoff] will feel like a practice round, and I will feel more comfortable because I am playing against [someone who is] the same age.''
Pak's big hole yesterday might have been the par-4 ninth, where she made a major mistake trying to hit an approach shot out of deep rough, over water and onto the green. In fact, she barely made it to the water.
But after taking a drop, Pak hit a pitch over the water to 4 feet and sank the putt for bogey.
``It was deep rough and a bad lie,'' she said, ``but I wanted to try.''
The winner of today's playoff will become the youngest player ever to win the Open. Chuasiriporn, whose 21st birthday falls on Thursday, is slightly older than Pak, who won't be 21 until Sept. 28. Catherine Lacoste was 22 when she became the only amateur to win the Open, in 1967.
Pak already has finished the weekend with one victory. Because Chuasiriporn is an amateur, the $267,500 first-prize check goes to Pak, even if she finishes second today.
That, however, wouldn't satisfy Pak.
``I don't want money, but I want the trophy,'' she said.