World number one Ko Jin-young of South Korea fired a bogey-free seven-under-par 65 to seize a one-stroke lead after Thursday's first round of the LPGA JTBC Classic.
Coming off her 13th career LPGA title three weeks ago at Singapore, Ko closed with three consecutive birdies to grab the top spot after 18 holes at Aviara Golf Club in Carlsbad, California.
Ko, whose parents are visiting and cooking her dinner every night, completed her 31st consecutive under-par LPGA round and her 16th in a row in the 60s.
"It feels great to record like one step at a time," Ko said. "I'm just trying to hit 60s today. These greens are really tricky so I didn't expect I'd make a lot of putts on this green, but I made a lot."
Denmark's Nanna Koerstz Madsen was second on 66 with American Cheyenne Knight, Scotland's Gemma Dryburgh and South Korean Choi Hye-jin on 67.
Ko, who started on the back nine, birdied the par-4 12th, par-3 14th and par-4 16th, then reeled off six pars in a row before a birdie at the par-5 fifth and three in a row at the par-4 seventh, par-5 eighth and par-4 ninth to close hr round on top.
"My mental (game) is strong right now," Ko said. "I can feel it growing, before Singapore. I have a lot of confidence.
"I love to play golf right now. I'm really enjoying it right now. Shot by shot I can feel confidence 100% and I can focus 100% for my ball."
Ko won two major titles and four LPGA victories overall in 2019 but says her best is yet to come.
"It's not coming yet," she said. "It's coming soon maybe. Even this year. I need to win more and I want to win more. But I have to focus on myself if I want to really get the wins."
Madsen, another back-nine starter, opened her front and back nines with back-to-back birdies, answered her lone bogey at the fourth with a birdie at the fifth and eagled the par-5 eighth to finish one off Ko.
"I'm very pleased with the score," the Dane said. "I made some good putts out there, which I maybe wasn't expecting only having 25 putts today, but it was good."
A sixth-place pack on 68 included New Zealand's third-ranked Lydia Ko, Americans Mo Martin and Ryann O'Toole, Canada's Maude-Aimee Leblanc and Thailand's Pajaree Anannarukarn.
LPGA JTBC Classic scores
65 - Ko Jin-young (KOR)
66 - Nanna Koerstz Madsen (DEN)
67 - Cheyenne Knight, Gemma Dryburgh (SCO), Choi Hye-jin (KOR)
68 - Mo Martin, Maude-Aimee Leblanc (CAN), Ryann O'Toole, Lydia Ko (NZL), Pajaree Anannarukarn (THA)
69 - Alana Uriell, Kim In-kyung (KOR), Minjee Lee (AUS), Danielle Kang, Ariya Jutanugarn (THA), Charley Hull (ENG), Stephanie Meadow, An Na-rin (KOR), Emma Talley, Moriya Jutanugarn (THA), Jessica Korda, Leona Maguire (IRL), Chun In-gee (KOR), Atthaya Thitikul (THA), Alison Lee, Kang Haeji (KOR)