An early start to the day saw Ko largely avoid the harsh heat at the Mission Hill Country Club, where temperatures can reach the 30s.
The cooler conditions were welcomed by the Kiwi.
"Nice to be able to play in the morning," Ko says. "This morning was probably the most chilly out of all of the mornings I've been here."
Ko is pleased with the way she was striking the ball.
"I gave myself a lot of good looks for birdies and I think that's going to be the key not only at this event, [but] especially at majors," she adds.
"It makes it a slightly stress-free par."
"All you can do is commit and hit a good shot, a competent shot."
Ko was steady in her final nine holes, with eight consecutive pars before a birdie on her 18th, lifting her into the top 10 on the leaderboard. It leaves Ko with a good amount of confidence for the next three rounds.
"I'm just going to go out there and be committed, and just hit it aggressively and confidentially. It's not easy out here, with the Bermuda glass it plays a lot differently.
"The greens were a lot faster today than when I played the practice rounds.
"I thought yesterday was the fastest out of the other days and today was significantly faster."
"It just makes it tougher but it's nice to putt on these greens."
The second of the women's five golf majors, held near Palm Springs in California, usually takes place in April, but the Covid-19 pandemic has seen the event pushed back.
It is a time of year where heat waves ravage the state, and will add an extra wrinkle for players over the weekend.
Meanwhile, Tim Wilkinson has fired a five-under par 66 in the first round of the PGA Tour's Safeway Open in California. He's tied for 11th, four shots off the lead.
At the European Tour's Portugal Masters, Ryan Fox is tied for ninth, six shots off the lead after carding a four-under 67.
