The world number 186 Wichanee Meechai fired a six-under-par 66 to share the lead with Sweden's Maja Stark after the first round of the LPGA Shanghai on Thursday.
Danielle Kang, who won the $2.1 million event the previous times it was held, in 2018 and 2019, shot a bogey-free 68 for a share of third.
Another American, world No 1 Lilia Vu, struggled to par for a share of 37th at Qizhong Garden Golf Club, where it was grey for much of the day and the heavens opened in the mid-afternoon.
World No 2 and home favourite Yin Ruoning carded a 71 for a share of 27th.
The 30-year-old Wichanee of Thailand shot two eagles and four birdies, offset by two bogeys, to take a surprise two-shot lead with Stark.
Wichanee has never won on the LPGA Tour but said she felt at home in Shanghai having played the course before and been on China's golf tour.
But she only arrived in Shanghai on Tuesday and said: "I haven't practised actually, but it just feels like home. Feel like I'm used to the vibe."
The 42nd-ranked Stark was more consistent with six birdies and no bogeys.
Maja Stark and Wichanee Meechai lead the field after 18 holes at the Buick LPGA Shanghai!
— LPGA (@LPGA) October 12, 2023
FULL LEADERBOARD ⬇️ https://t.co/XhLuW0qU1m
Ten players were in a tie for third, including Kang and the Thai duo of Pavarisa Yoktuan and Jasmine Suwannapura.
Kang said she also felt right at home.
"It was a very solid day," she said.
"There are some holes where I know I needed to be, and I think having course knowledge, and having won here has really helped me out today."
The home charge was led by Cai Danlin, Li Shuying and Liu Yu, also on matching four-under 68s.
The LPGA event is the first international golf tournament back in China after a gap of four years because of the Covid pandemic.
Four of the top 10 players in the world are in action.