Former world number one Ariya Jutanugarn had a disastrous front nine in the first round of the Honda LPGA Thailand on Thursday, chalking up four bogeys before she ended on two over par.
Australia's Su Oh kept her cool in hot, sticky conditions to share a three-way tie for the lead.
The 25-year-old Oh fired a nine-under-par 63 with no dropped shots to sit alongside Japan's Nasa Hataoka and Esther Henseleit of Germany at the Siam Country Club in the beach resort of Pattaya.
China's Lin Xiyu leads the chasing pack on eight under, with another six players just a shot back in a tightly packed field.
On her fourth visit to the course, Oh said she battled to stay cool and hydrated in the sapping heat and humidity.
"It's so hard. Like I'm so done after the round," she said.
"It's just so hot and sticky. Just can't escape it."
The course typically favours long hitters but Oh, still chasing her maiden LPGA Tour victory, attributed her first-round success to her slick putting.
Meanwhile Lin was also pleased with her performance after hitting 18 greens on her way to 64.
"I'm very happy with the bogey-free first because that's always a bonus. It's a good sign of solid play," she said.
US star Danielle Kang, ranked fifth in the world, managed a clean if unspectacular round of 66, chalking up six birdies including three on the trot in the back nine.
But there was disappointment for Thailand's defending champion and former world number one Ariya Jutanugarn, who had a disastrous front nine chalking up four bogeys and ending on two over par 74.