In the first Ladies Professional Golf Association major of the year, the 21-year-old from Thailand - who made her Tour debut last year and has yet to win an event - played controlled golf in a third round that took place in 100-degree heat and wind at the Mission Hills Country Club in California. 

South Korea's defending champion Mirim Lee and Ally Ewing of the United States lie second at nine-under on 207, in an event being played without spectators for the second time in seven months.

"It's a great day," Tavatanakit, who is outside the top 100 in the women's world rankings, said after her round.

"[But] it's in the past now.

"All I can think about is what can I do tomorrow, what can I improve from today's round?

"I was getting a little tired at the end.

"What can I do to keep my energy level up throughout the day tomorrow?

"That's going to be my goal."

Lee stayed in contention to retain the title she won last September with a third round of 68, while Ewing moved up with a 66.

Shanshan Feng, the only player from China to have won an LPGA major, sits on 208.

She is one shot ahead of seven-time major winner and Rio 2016 champion Inbee Park of South Korea, and England's Charley Hull.