Choi made four straight birdies from the 15th hole, while Korda picked up five shots on her first eight holes. Neither made a bogey.
Third-ranked Stacy Lewis of the United States was in a tie for third place after a 68, along with South Koreans Hee Young Park and Hee Kyung Seo.
Top-ranked Inbee Park of South Korea was one of eight players a further stroke back after bogeying two of her first four holes before recovering with six birdies.
The event is the first LPGA tournament in China.