Twenty-year-old South Korean Pak Se-ri became the youngest US Women's Open champion when she beat American amateur Jenny Chuasiriporn at the 92nd hole at Blackwolf Run in Wisconsin yesterday. Pak and Chuasiriporn were tied at two-over-par 73 at the end of their 18-hole play-off before Pak won in sudden death two holes later when she sank a 15-foot birdie putt.

The LPGA rookie became not just the youngest champion of the most important title in women's golf, but also the youngest woman to win two majors in the same year.

Two months ago she won the LPGA Championship and her US Open victory confirmed her arrival as a superstar.

But Pak had to work hard to come from behind and beat Chuasiriporn, a third-year student at Duke University in Durham, North Carolina.

Three days before her 21st birthday, Chuasiriporn was seeking to become just the event's second amateur champion, and for a long time she looked like doing so.

She opened a four-shot lead after five holes, but crashed with a triple-bogey at the par-three sixth, where she lost her ball in a hazard short of the green.

Chuasiriporn still led by two strokes after 10 holes, but Pak made her move with birdies at 11, 12 and 14 to go ahead, before bogeying the 15th to fall back into a tie.

They remained tied going to the par-four 18th, where Pak pulled her drive into a hazard. Her ball stopped in long grass but she was able to play it - while standing in the water.

She made bogey from there, leaving Chuasiriporn with a chance to win it, but the amateur also bogeyed after hitting a poor chip and missing a 10-footer for par, forcing the sudden-death extra holes.