Gabriela Ruffels remains in the hunt for her maiden tournament win. She's the leading Australian and four shots off the pace, in a tie for ninth at 12 under after her 67 on moving day.
Compatriot Minjee Lee (71) sits at nine under, with Roby Choi (70) and Steph Kyriacou (70) seven under, Hira Naveed (70) four under and Grace Kim (75) three under.
Hull birdied four of her final eight holes to post 16-under 200 at TPC River's Bend on Saturday, and credited her straightforward mental approach.
"I just hit a ball and find it and hit it again, you know what I mean? I think that's the trouble with many golfers, overthinking," Hull said.
"It's just a game. Hit a white ball at the pin. Make a birdie or make a par, make a bogey, whatever, just roll on to the next hole."
Thitikul, seeking to become the first multiple winner on the LPGA Tour this season, shot 68. The Thai star won in May at Liberty National in New Jersey.
Hull has two LPGA victories, most recently in 2022. The English player is coming off a runner-up finish in Houston on the Ladies European Tour.
"Just kind of not even thinking about tomorrow. Looking forward to my fish tacos later tonight," Hull said.
Two Japanese players with victories this year are two shots back. Women's British Open champion Miyu Yamashita (66) and rookie Chisato Iwai (66).
Second-ranked Nelly Korda, who is winless this year, closed with an eagle on the par-5 18th to shoot 68 and was three shots back alongside fellow American Yealimi Noh (64), the Philippines' Bianca Pagdanganan (66) and China's Mary Liu (68).
Second-round leader Chanettee Wannasaen of Thailand faded with a 75 and is six shots back.
With AAP.
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