The West Australian sank a 45-foot putt on the 18th hole at Siam Country Club to card a six-under-par 66 for a shot lead with 2016 champion Lexi Thompson, Jessica Korda and local hope Moriya Jutanugarn.

"I just hit the collar. I didn't know if I was going to have enough. Such a big break there. I'm glad it caught the hole," Lee said.

"It's a second-shot golf course. Your approaches are really important and obviously being in the right spots with the undulation. And if you have a hot putter that's going to help."

Lee won the Vic Open this month and opened her 2018 LPGA Tour account last week at the Women's Australian Open, finishing fifth.

Lee looks on during the Honda LPGA Thailand at Siam Country Club in Chonburi, Thailand. PHOTO: Thananuwat Srirasant/Getty Images.

Thompson, who won the Thai event in 2016 by six shots with a 20 under total and tied for fourth last year, started her round in style with an eagle followed by a birdie only to bogey the 3rd hole.

She shot four more birdies.

"It definitely helps to get that kind of start but I was just trying to keep that momentum and not get ahead of myself," Thompson said.

Her compatriot Korda had a rollercoaster round which featured eagles on the 1st and 17th holes, five birdies, a double bogey on the 6th and two bogeys.

Moriya was the only player among the four to end the day without a bogey.

"I had a good start today, it was better than I expected," said Moriya, who was seventh last year.

She's trying to become the first Thai winner of the tournament.

Two-time champion Amy Yang and World No. 2 Sung Hyun Park were among six players at five under.