The tournament is the first event on the 2013 LPGA schedule.
Ko owns wins in three professional tournaments, including last week's New Zealand Open. She had 11 birdies, an eagle and three bogeys in her round Thursday for a one-stroke lead over Mariajo Uribe, who had seven birdies and an eagle in shooting 64.
Jiyai Shin is third at 8-under 65 while Lee Mi-hyang, Rebecca Lee-Bentham and Ayako Uehara are tied at 7-under.
Ko, opening on the second nine of the Royal Canberra Golf Club, hit her first shot into the trees and ended up with a bogey but then reeled off four consecutive birdies and capped the spurt by dropping in a 100-yard wedge shot for an eagle at the par-5 15th.
She had another bogey at 16 but closed the side at 6-under 30 with two birdies. Ko added four birdies over Nos. 2-6 and went bogey-birdie in her final two holes of the first round.