World no. 1 Vu endures difficult start to LPGA Thailand defence
Taiwan's Chien Peiyun fired a 64 to lead the $1.7 million tournament after the first round at Siam Country Club Pattaya.
Ranked 113th in the world, Chien was two shots clear of South Korea's Kim Sei-young, with eight players including Korean compatriots Kim Hyo-joo and Jenny Shin carding 67s.
The American Vu came into the tournament fresh off a fabulous 2023, kick-started by her performance in Thailand this time last year.
The 26-year-old went on to win major crowns at the Chevron Championship and British Women's Open.
Vu started her Thailand defence off well, carding three birdies in her opening seven holes, before her round went awry.
Successive bogeys at the 10th and 11th holes were then followed by a dispiriting three more.
Vu at least ended her disappointing day on a brighter note with a birdie at the 18th.
In contrast, leader Chien was in fine touch.
The 33-year-old fired seven birdies and also an eagle, at the par-five seventh, against a lone bogey at the 14th.
"I wish I can play like this every day," she said.
"I'm very happy. Just keep the good memory."