World-ranked 470 Natthakritta Vontaveelap grabbed a shock lead at the halfway stage of her home LPGA Thailand on Friday to upstage a slew of big names including Lydia Ko.
The 20-year-old Thai rookie only turned professional in November and is contesting her first LPGA event after getting a sponsor invite.
But if she was nervous she did not show it, carding a seven-under-par 65 in the second round at Siam Country Club Pattaya for a one-shot lead.
Sweden's Maja Stark was second on 11-under overall after her 67.
Nelly Korda, America's world number two, was two shots off the lead along with four others.
Top-ranked Ko, the New Zealander who has been in red-hot form, was four shots off the lead in a share of 15th.
Natthakritta, who fired eight birdies against one bogey, said: "I feel excited to play in front of Thai (fans). This is my first time, you know. It's my largest (crowd)."
Ko surged into the lead of the 1.7-million-dollar event after three birdies in her first four holes and she picked up three more, but she faltered on the back nine with a bogey and double bogey.
The Seoul-born 25-year-old settled for a four-under-par 68, just as she had done on the opening day.
The 23-year-old Stark was pleased with how she handled the occasion after grabbing sole ownership of second place.
"I've been trying to get better at handling nerves, but I feel like I'm going to have nerves the whole weekend, so I'm just going to keep playing aggressively anyway," she said.
Korda's sister Jessica won the same tournament in 2018 and she hopes to take home a matching title.
"It would be great. Still 36 holes away from that," said the 24-year-old after her round of 66 left her ominously placed.
LEADING SECOND-ROUND SCORES
132 - Natthakritta Vongtaveelap (THA) 67-65
133 - Maja Stark (SWE) 66-67
134 - Jaravee Boonchant (THA) 65-69, Nelly Korda (USA) 68-66, Emily Pedersen (DEN) 67-67, Céline Boutier (FRA) 68-66, Shin Jenny (KOR) 66-68
135 - Yuka Saso (JPN) 67-68, Pornanong Phatlum (THA) 70-65, Anna Nordqvist (SWE) 65-70, Frida Kinhult (SWE) 67-68, Leona Maguire (IRL) 67-68, Jodi Ewart Shadoff (ENG) 69-66, Georgia Hall (ENG) 67-68
136 - Charley Hull (ENG) 69-67, Lydia Ko (NZL) 68-68, Atthaya Thitikul (THA) 67-69, Danielle Kang (USA) 70-66, Lilia Vu (USA) 66-70
137 - Jennifer Kupcho (USA) 65-72, Ashleigh Buhai (RSA) 72-65, Saki Baba (JPN) 69-68, Nasa Hataoka (JPN) 65-72, Carlota Ciganda (ESP) 69-68, Kim Sei-young (KOR) 69-68, Kim Hyo-joo (KOR) 67-70