Soo-Jin Yang matched the course record under 65 and she took a one-stroke lead after two rounds of the LPGA HanaBank Championship.
Yang, a three-time winner on the Japan LPGA, completed 36 holes at 10-under- par 134. This is just her third start on the LPGA Tour, having competed at this event last year and at the U.S. Women's Open earlier this season.
Tseng recovered from a tough start to shoot two-under 70, while Choi carded a four-under 68. They share second place at minus-nine at Sky 72 Golf Club's Ocean Course.
The LPGA Tour began its Asia swing one week later than expected this year after The Imperial Springs LPGA was canceled last week. Tournament officials were unable to get proper permits for the tournament in time, but this week's event went on as planned.
Yang got off to a flying start as she birdied the second and third. After a par on the fourth, she posted back-to-back birdies from the fifth to jump to minus-seven.
She parred four in a row from the seventh. Yang converted a birdie effort on the 11th, then parred her next three holes. She claimed the top spot with birdies on the 15th and par-five 18th.
"I had a really good feel for my shots starting yesterday," Yang said through a translator. "I missed a lot of shots and opportunities out there yesterday, but was able to capitalize on those chances today."
For the second straight day, Tseng stumbled out of the gates. On Friday, she bogeyed the first and third. She opened Saturday's second round with bogeys on two and three to slide to minus-five.
Tseng quickly rebounded as she poured in four consecutive birdies from the fourth. She dropped another stroke on the eighth to turn at eight-under.
Birdies on the 11th and 15th gave Tseng a piece of the lead, but she faltered to a bogey on No. 16 to fall one back. That is where she ended after parring the final two holes.
"I made lots of mistakes today. I just didn't finish the way I wanted to," Tseng admitted. "Hopefully tomorrow will be better."
Choi had two birdies on the front nine, both of which came on par-threes. Around the turn, she birdied a pair of par-fours, the 11th and 15th, to get to minus-nine. She parred the last three holes to cap a bogey-free round.
Jimin Kang (69) and Chella Choi (71) share fourth place at seven-under-par 137. Meena Lee carded a two-under 70 and is one stroke back at minus-six.
NOTES: Na Yeon Choi would become the ninth LPGA Tour player to three-peat if she can rally for the victory on Sunday...Lorena Ochoa was the last to win the same event three straight years when she won the Sybase Classic from 2006-08...Choi birdied the final hole in 2009 to beat Tseng for this title...Cristie Kerr bounced back from her wrist injury at the Solheim Cup to play this week, but she is well off the pace after rounds of 72 and 70.