Lydia Ko had the best round of her LPGA Tour career at the Ford Championship to take a narrow lead after the first round in Phoenix.
Opening with four straight birdies, Ko closed with two more birdies for a 12-under 60 on a day of extreme low scoring.
Defending champion Hyo Joo Kim shot a 61, making it the first time since the 2003 Kellogg-Keebler Classic that two players were double digits under par in the opening round.
"I don't think I've ever actually started a round with four birdies, so it was nice to take advantage of the good start and continue that on my back nine," Ko said.
"Like every golfer, when things go well you also think about the things that could go terribly wrong. I feel like I stayed patient and was rolling it really well."
A moderate start to her 13th season came to life on the Cattail course at Whirlwind Golf Club when the 28-year-old Ko got into a rhythm after a rare putter change and started piling up the birdies.
She said the idea of 59 - Annika Sorenstam has the only sub-60 round in LPGA history, 25 years ago on a different course in Phoenix - entered her thinking when she birdied her 14th and 15th holes of the round.
But she didn't hit a seven-foot birdie putt firmly enough on the par-five seventh. Ko finished with two more birdies for her career-low round.
"That would have been nice to hole that one," Ko said. "But who knows? Maybe if I holed that one I might not have holed the other two. You can't think about 'what if?' Birdied some other ones that I didn't expect, so kind of just evens out in that sense."
It was the ninth round of 60 or lower on the LPGA, the most recent by Lucy Li at Pinnacle Country Cub in Arkansas in 2024.
Kim also started on No 10 and shot 28 on the front nine, finishing birdie-eagle-birdie, including a hole-out from the fairway on the par-four eighth hole.
Nelly Korda, who opened the year with a 54-hole win in Florida and was runner-up last week in California, holed out from the 18th fairway for eagle in the middle of her round and shot 63, one of her career best.
They all played in the morning and no one caught them in the afternoon, when temperatures were pushing 38 degrees Celsius.
Frida Kinhult of Sweden had a 64, the low score of the afternoon, while Jeeno Thitikul, the No 1 player in women's golf, opened with a 69.
