The 20-year-old carded seven birdies and a hole-out eagle on the par-4 10th at TPC River’s Bend to establish a two-shot advantage. Wannasaen did not drop a shot all day, capitalising on soft conditions and minimal wind to post her lowest round on the LPGA Tour this season.

American Gigi Stoll sits outright second after a 65, while six players are tied at six under, including major champion Patty Tavatanakit, Korea’s Sei Young Kim, and American rookie Jenny Bae.

"I think they're a little shorter than usual, so playing the par 5s well out here is going to be a big advantage," Stoll said via the LPGA Tour website.

"I just got the ball rolling today."

World No.1 and defending champion Nelly Korda remains firmly in contention after signing for a five-under 67. Korda mixed eight birdies with three bogeys and is part of a larger group four shots behind the leader.

Australia also made its mark on day one. Gabriela Ruffels matched Korda’s score with a composed 67 to share ninth position, continuing her consistent season on the LPGA Tour. Grace Kim, Steph Kyriacou and Minjee Lee are two shots further back after rounds of 69, giving both players a strong platform heading into the second round. Their performances ensured three Australians finished inside the top 20 on a day when low scoring was widespread.

England’s Charley Hull and rising star Lottie Woad also began strongly, each carding rounds of 68 to position themselves well within the top 20.

Play continues Friday morning local time, with the top 65 and ties advancing to the weekend.