Lexi Thompson, a 19-year-old Floridian, fired an eight-under 64 on Friday to join Se Ri Pak for the second-round lead of the Kraft Nabisco Championship.
Thompson had eight birdies and no bogeys during her round at Mission Hills Country Club in Rancho Mirage. She and Pak were both at seven-under 137 after two rounds.
"I was just trying to stay in the moment and ... not think about what I was shooting," said Thompson, who has three LPGA wins but is yet to win a major event.
The Kraft Nabisco Championship is the first LPGA major tournament of the season, and Pak, the veteran South Korean, is hoping to win the sixth major of her career.
Pak, 36, shot a two-under 70 to maintain a share of the lead. After seeing Thompson's score, Pak said simply, "That's amazing."
Michelle Wie was one shot behind the leaders after shooting a one-under 71. First-round leader Shanshan Feng of China, also at six-under for the event, teed off later Friday.
Catriona Matthew of Scotland shot a four-under 68 and was three shots behind the leaders at four-under par.
Morgan Pressel, who won the Kraft Nabisco in 2007 at age 18, also was at four-under for the tournament after shooting a two-under 70.
Angel Yin, a 15-year-old amateur from Arcadia, also was at four-under and had yet to tee off Friday.