World number one Jeeno Thitikul carded a nine-under-par 63 to open up a three-shot lead after two rounds of the LPGA’s season-ending CME Group Tour Championship.
The 22-year-old from Thailand made four consecutive birdies either side of the turn in her bogey-free round to reach 14 under overall in Florida.
Thitikul is aiming to win the most lucrative tournament in women’s golf – which has a top prize of $4m (£3.1m) – for a second consecutive year.
South Korea’s Kim Sei-young is at 11 under, while Japan’s Nasa Hataoka is a shot further back along with first-round leader Somi Lee.
Home favourite Nelly Korda, who struggled on Thursday, is also firmly in contention after surging up the leaderboard with a 64.
The two-time major champion, who has not won an event this season, made nine birdies including three in her final four holes to end Friday in a tie for fifth.
Korda said some minor adjustments to her putting made the difference after she managed just three birdies on the opening day.
“On Thursday I was just missing by centimetres,” Korda said. “They were burning edges, lipping out.
“This has been kind of the common theme this year. I feel like I played so much better than my score has shown.
“So I honestly just went to the putting green for five minutes and simplified it.”
Denmark’s Nanna Koerstz Madsen is the highest placed European at eight under with England’s Charley Hull frustratingly making three bogeys alongside six birdies in her round of 69.
It leaves England’s Hull at six under – eight shots adrift of Thitikul – with her compatriot Lottie Woad at five under.
The LPGA’s concluding event of the season carries a total purse of $11m (£8.4m).