SAN FRANCISCO, 24 Apr 2015 (AFP) - The world number one from New Zealand looked confident and comfortable in the first round much like she did last year when she picked up her first professional win at this event.
"I read most of (the greens) really well," Ko said. "I tried to be confident with the reads I had. It's tough here so you can't really be overly aggressive."
Ko, who turns 18 on Friday, has won six times on the LPGA Tour. Her first win came at the 2012 Canadian Open as an amateur.
Juli Inkster, 54, posted a four-under 68 and she is tied for second, one stroke behind Ko at Lake Merced Golf Club. The 2015 Solheim Cup captain is joined there by Jang Ha-Na of South Korea and Thailand's P.K. Kongkraphan.
Inkster hasn't won an LPGA Tour event since capturing her 31st career victory in 2006.
"Age matters in a lot of things, as far as how your body feels, how far you hit the ball and how much time you can put into it -- but you can still go out there and compete at 54," Inkster said.
World number two Stacy Lewis headlines a group of four players tied for fifth at three under. Lewis finished the first round alongside Morgan Pressel, Caroline Hedwall and Choi Na-Yeon.
Ko began her round with four straight pars before making her way up the leaderboard.
Inkster, Jang and Kongkraphan all shared the clubhouse lead early on. Ko pulled even with the trio with four birdies in five holes from number five.
Following a par at 10, Ko briefly dropped back to three under for the day with her lone bogey at the par-four 11th.
Ko then took the lead for good when she drained back-to-back birdies on 13 and 14, getting her to five under. She ended her day with four consecutive pars to finish with a 67.
Jang started quickly making five birdies and two bogeys on her front nine along with two pars. On the back nine she rolled in three more birdies and two bogeys.
Leading first-round scores on Thursday at the LPGA Tour's Swinging Skirts Classic (USA unless noted, par-72):
67 - Lydia Ko (NZL)
68 - Juli Inkster, Ha Na Jang (KOR), P.K. Kongkraphan (THA)
69 - Morgan Pressel, Na Yeon Choi (KOR), Stacy Lewis, Caroline Hedwall (SWE)
70 - Julieta Granada (PAR), Pornanong Phatlum (THA), Shanshan Feng (CHN), Anna Nordqvist (SWE), Tiffany Joh, Chella Choi (KOR), Moriya Jutanugarn (THA), Yueer Feng (CHN), Brooke Henderson, Andrea Lee