They were one stroke ahead of another local favourite Ariya Jutanugarn and Denmark’s Nanna Koerstz Madsen who were tied for third in the US$1.6 million (B50mn) tournament, which was cancelled last year due to the COVID-19 pandemic.
The 2021 edition is being held behind closed doors under strict coronavirus protocols at Siam Country Club.
ANA Inspiration winner Patty, whose Thai name is Paphangkorn, rolled in the last of her nine birdies on the par-five 18th hole to surge ahead.
The only blip for the 21-year-old LPGA Tour rookie on a hot day was a double bogey on the sixth hole.
Fresh from a T3 finish in Singapore last week, the Bangkok native said her momentum started when she birdied the opening hole and made a putt from off the green for another on the third.
“It was a solid round today. I didn’t expect to shoot this low. I wasn’t feeling my best,” said Patty, who claimed her maiden LPGA win at the ANA Inspiration last month.
“I feel like that my putts went in as my speed and reading [of the greens] was pretty good the whole day. I feel like I judged everything really well and I’m pleased with my round today.”
It is Patty’s first appearance in the LPGA Thailand as a professional, having played in the tournament twice as an amateur.
Atthaya, 18, also excelled in the heat with two eagles - on the 10th and final holes - to stay in contention for her first title on the LPGA Tour.
Atthaya, who like Patty is competing in her third LPGA Thailand and first as a pro, carded her career-best 18 holes on tour.
“I had an amazing round today - two eagles in one day,” said the Ratchaburi native, who won two Ladies European Tour event when she was still an amateur.
“Today it was so hot but I just tried to keep my momentum going, keep rolling the putts. I gave myself a lot of chances to make birdies. If I made them that was good, if not I just continued. I’m used to the heat but I don’t know the course that well.”
The teenager said she had never made two eagles in the same round before, and was surprised by how well she was able to chip.
“For holes No.10 and 18, I did not think that it’s going to go in - I just took it as easy as I could,” said Atthaya, who has won six domestic tournaments since turning pro last year.
“I am not a good chipper so at 18 I decided to putt. At 10, I shot it and was surprised how good it was.”
Two-time major winner Ariya made eight birdies but a bogey on the 18th ruined her chances of joining her compatriots at the top.
No Thai has won the LPGA Thailand since it was launched in 2006.
Madsen carded one of six bogey-free rounds recorded yesterday. In all, 53 of 72 players finished the day at even par or better, including three-time winner and defending champion Amy Yang.
The South Korean rebounded from four bogeys and one birdie on her front nine to card six birdies on her final nine holes for a three-under 69.