Former world number one Lydia Ko, seeking her first win since 2016, fired a four-under par 68 on Thursday to head a group of five players sharing the first round lead in the LPGA Mediheal Championship.
On the same Lake Merced Golf Club course where she won in 2014 and 2015, New Zealand's Ko carded an eagle and three birdies with just one bogey.
"Wind is probably the biggest factor on this golf course," said Ko, who celebrated her 21st birthday on Tuesday. "It's a golf course where nobody goes super low, so you just have to keep continuing to play solid and be patient out there and sometimes par is not a bad score."
Patience was at even more of a premium in the chilly, windy weather, with afternoon starters getting the worst of the gusts.
Four of the five leaders played in the morning wave -- Ko, Sweden's Caroline Hedwall, South Korean Kim In-kyung and American Jessica Korda.
Australia's Su Oh joined them late, and was the only player in the group without a bogey on the day.
England's Charley Hull, South Korean Kim Sei-young, France's Celine Herbin and American Lexi Thompson were a stroke back on 69.
"It was cold and pretty windy out there, and because it's got a lot of elevation, it kind of swirls in the middle like in the low areas, so it was tough," Oh said. "I hit the ball really solid today, and then the ones I missed I made really good up-and-downs. I'm really happy with my round."
Oh, who missed the cut in five of her eight starts this season, said a switch to heavier shafts had worked out well.
"Hopefully it will keep working," she said.
For Ko, a return to Lake Merced is a return to a course that featured prominently in her precocious rise to stardom.
Her first win here in 2014 was her first as an LPGA Tour member.
The New Zealander has 14 LPGA titles, including two majors and has spent 104 weeks at number one on the world.
But she hasn't lifted an LPGA trophy since the Marathon Classic in July 2016 and is now 18th in the world.
"I know this is a golf course where I've played well at," she said. "The fans have been amazing, they've been super supportive every single time I've come here.
"I hit a lot of greens, so I'm giving myself many opportunities for birdies, and this is a golf course where you need to drive the ball well and putt well."