Tavatanakit crushed drives — hitting a 337-yarder on the par-five 11th — and was equally as effective on and around the greens.
"I've hit it the farthest I've ever hit here," Tavatanakit said. "It's a little strange to have a lob wedge in on the first hole."
The former UCLA star is trying to become the sixth straight international winner in the tournament celebrating its 50th edition. She won seven times in two seasons at UCLA and had three second-tier victories in 2019.
"Keep on the pedal," Tavatanakit said. "I play aggressive when I can be and you got to play smart golf. It's a major championship. Pins are tough, tough conditions. You got to have the things you need to go out and execute and embrace all the challenges."
Lee shot a 68, wearing a facemask while she played. The South Korean player won the postponed event in September for her first major title. Ewing had a bogey-free 66. The American won last year at Reynolds Lake Oconee for her first tour title, playing then under her maiden name of McDonald.
"I was able to get off to a really good start with three birdies to start the day," Ewing said. "Then I just kept giving myself a lot of looks."
Shanshan Feng, a stroke behind playing partner Tavatanakit entering the round, was at eight-under after a 72.
- With AP