American Danielle Kang closed with back-to-back birdies to match New Zealand's third-ranked Lydia Ko for the lead after Friday's chilly second round of the LPGA at Boca Rio.
Kang fired a four-under par 68 to equal Ko, who grinded to a 70 in cold and windy conditions as both finished on 11-under 133 after 36 holes at the resort in Boca Raton, Florida.
"Played really well," Kang said. "Coming in 2-under the last couple holes I just really wanted to get to the double digits. That was kind of my goal today, so I was happy to do that."
Philippines-born Yuka Saso, now playing for Japan, and England's Jodi Ewart Shadoff were a distant third on 137.
Saso finished with a 2-under 70 on the day.
After winning last week's LPGA Tournament of Champions in Orlando for her 6th tour title, Kang trailed by 2 when the day began.
Kang started on the back nine and birdied the par-3 13th and par-4 14th, then made a birdie-bogey start to her second nine at the 1st and 2nd holes. She birdied the par-5 8th, playing a wedge to 7 feet and sinking the putt, and closed with a 10-foot birdie putt at the 9th to match Ko atop the leaderboard.
"I was actually just cold today," Kang said. "Just focused on finishing well. When I wake up and go outside and see how cold it is, I'll figure out how to dress and then attack it tomorrow."
Ko, who made an opening 63, made 4 birdies against 2 bogeys, but the 24-year-old South Korean-born Kiwi battled the weather as well.
"It was more of a grind out there," Ko said. "I don't think I played as solid compared to yesterday. I don't think I could have played much better than the first round.
"With it being a little windier and chillier, it did make the golf course a little longer. Having longer irons into the greens makes it a little tougher.
"The temperature plays a huge factor. I just tried to stay focused and play the best golf I can and give myself a lot of opportunities."
Ko said her mother struggled to find hand warmers, but added, "she was able to get some so I'm OK for now."
Ko birdied the par-3 third and followed a bogey at the 7th with a birdie to close the front nine. After a bogey at the 11th, she answered with birdies at 14 and the par-3 17th, calling the latter "a good way to finish."
Last year's Tokyo Olympic bronze medalist after taking silver in 2016 at Rio, Ko seeks her 17th career LPGA title and first since last April's Lotte Championship in Hawaii.
Sharing fifth on 138 were England's Bronte Law and Charley Hull, Japan's Nasa Hataoka, Swiss Morgane Metraux and India's Aditi Ashok.