The 16-year-old started her round on the 10th hole and was even through the first six holes before dropping a shot at the par-four 16th. Ko birdied the 18th to make the turn at even par but that was shortlived following a double bogey at the par-four first.
She gained a shot back with a birdie at the seventh hole to finish at one over.
One of the early players on the course, Ko's 73 placed her in a share of 15th with many big names yet to start their rounds.
China's Shanshan Feng was the clubhouse leader at six-under - a two shot lead over the field.
- nzherald.co.nz