Yuka Saso fired a second straight 64 to take a two-stoke halfway lead over former world number one Lydia Ko in the LPGA Lotte Championship on Thursday.
Saso, a 19-year-old from the Philippines seeking a first US LPGA title after two wins on the Japan LPGA, shared a one-stroke overnight lead with Brittany Altomare.
But she was six adrift when she teed off after New Zealand's Ko stormed up the leaderboard with a sensational nine-under par 63 that featured nine birdies without a bogey.
Undaunted, Saso was two under through the first two holes at Kapolei Golf Club in Oahu, Hawaii.
After her lone bogey of the day at the fourth she birdied the fifth, then charged with four birdies in a row at the seventh, eighth, ninth and 10th to tie Ko atop the leaderboard.
She snaked in a long birdie bomb at the 16th to gain the solo lead and drained a four-footer at 17 as she built a 36-hole total of 16-under par 128.
"I think I hit good tee shots today and holed a lot of birdie putts," said Saso, who added that the wind was "a little bit of a factor" on the back nine.
"I don't really like windy conditions," she said. "(But) I'm happy that I'm able to play good."
Trying to just "enjoy the moment" as she plays on a sponsor's exemption, Saso said she would try to just do my best again tomorrow" in pursuit of a first LPGA title.
At 14-under 130, Ko was alone in second and three clear of Spain's Luna Sobron Galmes, American Nelly Korda, and South Koreans Ryu So-yeon and Kim Hyo-joo.
"Today I feel like I gave myself a lot of good opportunities for birdies," said Ko, who came close to ending a three-year victory drought at the ANA Inspiration this month with a record-breaking 62 in the final round.
"Between yesterday and today I feel like my game has been pretty solid," she said. "So hopefully stick to my game plan and just keep hitting it confidently and with commitment and see where it takes me for the rest of the two days."
Of the group sharing third, Sobron fired 10 birdies, including five in a row, in an eight-under par 64.
Korda and Ryu both posted 68s while Kim reached 11-under with a 65 that featured an eagle at the 17th.
It was a further stroke back to a trio of players on 134, headlined by Women's US Open champion Kim A-lim.
Meanwhile, two-time defending champion Brooke Henderson of Canada, had work to do in her three-peat bid. She was six adrift after a second straight 68.