Former world number one Lydia Ko fired an eight-under-par 64 to take a share of the lead after the second round of the LPGA Tech Championship on Sunday.
Ko, of New Zealand, vaulted into a tie with American Lexi Thompson who is also at 15-under 129 with one round remaining in the tournament at the Brickyard Crossing course in Indianapolis.
The 20-year-old Kiwi, who is seeking her first win in over a year, birdied five consecutive holes in one stretch. She had nine birdies and one bogey in her round.
"I've enjoyed being in this position and being able to hit some good shots and give myself good looks at birdies," said Ko. "When you start doing that, it builds your confidence."
Taiwan's Candie Kung is alone in third after shooting a 64. Three strokes behind Kung is Ashleigh Buhai of South Africa, who stands at 11-under after shooting a 66 in the second round.
Cristie Kerr and Amy Olson are another stroke back at 10-under.
Ko started her round on No. 10. She had consecutive birdies on holes No. 2 through No. 6 on her back nine.
Ko began 2017 with four top-10 finishes in seven events. However, she has not finished higher than 10th in an event since then, and she missed the cut in two of her last three tournaments.
Thompson, the first-round leader, shot a six-under 66 in the second round and had to scramble to save par on her final two holes to grab a share of the lead in this three-round event.
Kung is well within striking distance, just a stroke behind the leaders after a round that featured nine birdies and one bogey.
"I've been playing pretty good golf this year but I just haven't been able to put them all together," said Kung, who has not won an LPGA event since 2008.
"Being able to put them together last week, four rounds, and then the last two rounds, it feels pretty good."
Anna Nordqvist of Norway was among those who failed to make the cut.