The surprise leader, in a field featuring 15 of the world's top 20 in the LPGA Tour's flagship Asian event, was Sarah Schmelzel from the United States.

The world number 107 found herself a stroke clear at the head of the field after a four-under-par 68 at Sentosa Golf Club .

Vu was in a three-way tie for second with Sweden's Linn Grant and Germany's Esther Henseleit.

South Korea's Ko Jin-young, who is seeking an unprecedented treble of titles after winning the 2022 and 2023 editions, is three shots back from Schmelzel in a 13-way tie for 10th place on a stacked leaderboard.

Starting from the 10th and turning at one-over par, Schmelzel, who joined the LPGA Tour in 2019, carded five birdies on a fabulous closing nine to take an opening-round lead for the first time.

"I have not been in this position before," Shcmelzel told reporters.

"But I guess there's a first time for everything. I'm excited. Let's see what happens next.

"This is my fifth (LPGA) year, so I'm just trying to get into contention more and get a little bit better every day," said the 29-year-old.

Vu expressed disbelief that no one posted lower than four-under par around the 6,775-yard Tanjong course that hosts the tournament dubbed "Asia's major".

"I was surprised that the scores were so high. I always expect at least six-under to be the leader. But that shows you how tough the course is playing and it's a good challenge," said Vu.

Vu found it tough to find birdies - she got into red numbers only at the third, sixth and 14th holes - in a bogey-free 69.

"The course is playing way more difficult than last year, and I knew that coming into today," said Vu, who won two majors in a breakout 2023 season.

"The greens are playing firmer and you can't hit to tucked pins.

"You have to take your medicine and just have a 20-footer to try and make a birdie," said Vu.