The 25-year-old from Bangkok, who is chasing her first victory on the tour, carded 10 birdies and four bogeys to finish the day with a six-under par 65 at Highland Meadows Golf Club in Sylvania.
Thidapa’s blistering round included seven birdies on the back nine, the last falling on the 18th to take her one stroke clear at the top of a congested leaderboard.
Even Thidapa seemed taken aback when informed later she had made 10 birdies in her round. “Did I make 10? Yeah, for real?” she asked reporters. “Oh wow.”
“I’m really happy about the way I played today,” she added. “There was a lot of drop on the back nine, and I just keep playing. I didn’t really look at the leaderboard, and did not even expect anything.”
A cluster of seven players were lurking menacingly on the world number 163’s shoulder on five under.
The chasing pack included South Korean stars Chun In-gee, Lee Mi-rim and defending champion Kim In-kyung, who all posted 66s.
Kim was unable to build on a dazzling performance over the front nine, which left her at five-under at the turn, with a bogey and a birdie on the back nine cancelling each other out.
“It was really exciting playing the front nine,” Kim said. “I had a good roll ... on the back, I hit a lot of good shots and good putts, just the greens can be tricky, and the wind was a little bit swirling. Overall it was a good round.”
Chun surged up the leaderboard after rattling in four consecutive birdies on her closing four holes. Also one off the lead were Sweden’s Caroline Hedwall, Taiwan’s Tseng Ya-ni and American duo Jacqui Concolino and Katelyn Dambaugh.
Eight players were two off the lead on four-under, including Canada’s Brooke Henderson, who made five birdies and one bogey in her 67.