Ko, Woad share lead at LPGA season opener
Ko rattled off a hat-trick of birdies on the back nine in a bogey-free round that left her on eight-under after 36 holes at Lake Nona Country Club in Orlando, Florida.
The 28-year-old three-time major winner was joined at the top of the leaderboard by England's Lottie Woad, who followed up her opening 67 with a three-under-par 69.
Ko said she had carried momentum from a solid opening round on Thursday into the second round.
"I felt like I played pretty solid overall," Ko said. "I surprised myself a little bit yesterday.
"I don't know what I was expecting, but I saw a lot of good and I think I just kind of carried on that momentum to today.
"I'm in a good position leading up to some tough golf ahead."
Rising English star Woad, meanwhile, who only turned professional last year after claiming a third place finish at the Evian Championship as an amateur, drained four birdies with only one bogey in her three-under-par 69.
Woad though was frustrated at her inability to shoot a lower score after missing a series of makeable birdie putts.
"Had a lot of eight-footers for birdie and just didn't make them, which was really annoying," the 22-year-old said.
Ko and Woad lead by one shot from South Korea's Amy Yang and Japan's Nasa Hataoka.
Hataoka had lit up the course with a six-under-par opening round on Thursday but had to settle for a 71 on Friday in a mixed outing that included three birdies and two bogeys.
Sweden's Ingrid Lindblad and South Korean duo Hwang You-min and Kim A-lim are a further shot back on six under.
Thailand's world number one Jeeno Thitikul is three off the lead on five-under alongside Nelly Korda and another Thai, Chanettee Wannasaen.