American Danielle Kang (30) fired a flawless nine-under-par 63 to grab a one-shot halfway lead at Sentosa after a weather-delayed second round of the HSBC Women's World Championship in Singapore on Friday.
World number 18 Kang, who finished in a share of 29th after the first round, surged to the top of the leaderboard of the Championship after draining nine birdies, including three in a row from the 12th.
Surprise overnight leader Elizabeth Szokol was tied for second place, alongside Allisen Corpuz and Kim Hyo Joo, after the world number 153 had an inconsistent round and nearly cancelled out her five birdies with four bogeys.
American world number two Nelly Korda was in a three-way share for fifth after carding 68.
After a difficult opening day with the putter, South Korea's reigning champion Ko Jin-Young shot eight birdies and a bogey to climb up to tied eighth with a seven-under 65, while top-ranked Lydia Ko (69) was in a share of 16th.