San Francisco, CA (SportsNetwork.com) - Defending champion and world No. 1 Lydia Ko fired a 5-under 67 in Thursday's first round and she grabbed the early lead at the Swinging Skirts LPGA Classic.

Ko is a six-time LPGA winner who picked up her first professional victory here last year. Her first two wins came at the 2012 and 2013 Canadian Open as an amateur.

"I read most of (the greens) really well. I kind of read two of them the other way, which was kind of odd, but other than that I tried to be confident with the read I had," Ko said about her putting. "It's tough here so you can't really be overly aggressive with it."

Juli Inkster, the 2015 Solheim Cup captain, carded a 4-under 68 and she is tied for second at Lake Merced Golf Club. The 54-year-old is joined there by Ha Na Jang and P.K. Kongkraphan.

World No. 2 Stacy Lewis headlines a group of four players tied for fifth at minus-3. Lewis finished the first round alongside Morgan Pressel, Caroline Hedwall and Na Yeon Choi.

Ko, who turns 18 years old on Friday, started off with four straight pars before her name suddenly emerged near the top of the leaderboard.

Chasing Inkster, Jang and Kongkraphan, all of whom shared the clubhouse lead early on, Ko quickly tied that trio with four birdies in five holes from No. 5.

Following a par at 10, Ko briefly dropped back to minus-3 for the day with her lone bogey at the par-4 11th.

Ko then took the outright lead for good when she drained back-to-back birdies on 13 and 14, getting her to minus-5. She finished up with four straight pars to end there.

"I didn't feel too tired after ANA (Inspiration), but now other people said I looked it on TV," said Ko, who has not played since finishing tied for 51st at the ANA Inspiration three weeks ago. "It just shows a sign that I needed that break and I definitely think it was worth it."

Inkster, playing the back nine first, rolled in a birdie at the 10th and later traded a bogey on 12 for a birdie on 13. Inkster made it four gains in five holes with a trio of birdies from 15, getting her up to minus-4.

After making the turn, Inkster drained her sixth birdie in 10 holes with a gain at one, putting her at 5-under. Inkster tripped to another bogey on three before finishing with six straight pars from four.

Jang started off on fire as she made five birdies and two bogeys on her front nine to go along with two pars. On the back side she holed three more birdies and two bogeys.

Kongkraphan made two bogeys in her first four holes and had four birdies in her first 10 at three, six, nine and 10. An eagle at the par-5 13th got her up to minus-4, where she stayed after finishing with four straight pars.

NOTES: Ko had three wins in the 2014 season and then won the Women's Australian Open earlier this year ... Ko has finished inside the top-10 in six of seven events this season, including two runner-ups and a third-place finish ... Jang and Kongkraphan are looking for their first LPGA victories ... Suzann Pettersen, who withdrew during the third round of last week's LOTTE Championship, withdrew before the start of this week's event. She was replaced in the field by Kelly Shon.