After a bogey at her first hole, the American bagged seven birdies and an eagle to build a solid lead over the chasing pack, which was led by Yuka Saso on five-under after the Japanese world number 36 shot a flawless 67.
American world number two Nelly Korda carded a 68 for a share of third place with five other players, including fellow major winners Patty Tavatanakit, Kim Hyo-joo, Ariya Jutanugarn and Lee Jeong-eun.
Top-ranked Lydia Ko of New Zealand and South Korea's reigning champion Ko Jin-young endured difficult days with the putter at the Sentosa Golf Club and finished in a share of 14th and 36th respectively.