Choi, just 16, said she felt "confused and let down" because her group of three had misinterpreted advice from a starter and had been wrongly taking preferred lies in the soggy rough during Thursday's opening round.

The Queensland-based Korean amateur, Sydney's Corie Hou and former Victorian junior champion Inhong Lim were disqualified en masse by a rules official on the second tee yesterday when Thursday's irregularities were raised by the girls themselves.

"I'm devastated and frustrated. We checked with a starter 100 per cent on what we were allowed to do ... I felt it meant (preferred lies) everywhere," said Choi, a Year 11 schoolgirl at Coomera's Saint Stephen's College.

"I was really happy with how I was going but I have to accept what has happened."

The former Australian junior champion said she had marked, cleaned and placed her ball in the rough three times during her two-under-par 70 on Thursday while Hou (81) and Lim (80) had done so a similar number of times.

The local rules sheet issued to all players in the wet lead-up to the tournament detailed preferred lies on "closely mown areas". Ladies European Tour operations director Cyprien Comoy said the trio had made a "genuine mistake" and it was a "harsh lesson learned because players have got to know the rules."

Choi will fly to Melbourne today to prepare for Australian Open qualifying on Monday and will be left to follow the birdie blitz of Korea's bubbly US Open champion Ryu (66-61) on television.

Ryu was superb yesterday, making a staggering 12 birdies and for a blink it appeared she might get within reach of a magical 59 despite a bogey hiccup on just her second hole.

She missed an eagle putt from a metre on the 3rd and a birdie chance on the 17th but rattled in sure putts aplenty and played a glorious, long bunker shot to set up birdie No.12 on the last.

Ryu is a delight at 21. Her ball carries a pink P mark. She giggles that it is all to do with her "Piggy" nickname.

"I'm a real food-est. My nickname is Piggy because my friends think I eat too much," she giggled.

"My coach (Brisbane-based Ian Triggs) says I'm 50 per cent Australian because I especially like Vegemite. I was told it was chocolate jam but after my strange face when I first tasted it, I love it."

Ryu revealed that "Piggy" means good fortune in Korea and her delight was obvious at shooting a career-best 61 to lead Dutchwoman Christel Boeljon (66-65) by four shots was obvious. Boeljon had a hot birdie-birdie-eagle finish of her own.