New Zealand’s Ko, at 17 the youngest golfer to claim the world No 1 ranking, was among the leaders after a delay pushed back the start of the round by four hours in Arizona.
Ko leads along with??Germany’s Sophia Popov and Americans Kim Kaufman and Tiffany Joh, with darkness halting play with half of the 132-strong field yet to finish.
Ko produced a round of seven birdies and one bogey, and said her score could have been lower – she has now broken par in 21-straight LPGA Tour rounds, a streak that started at last year’s season-ending Tour Championship.
“I think I had like three putts that were perfectly on line but I left it short, and that three-putt on seven,” she said. “But I guess everything balances out.
“I hit the pin with my chip in 18 – that could have been a much further par putt. So I think six-under is a good start and I just have got to take the positives out of it.”
Popov and Joh both posted rounds with six birdies and no bogeys, while Kaufman had seven birdies with one bogey to join the leading group.
They are one in front of South Korea’s Chun In-Gee and Thailand’s Moriya Jutanugarn, both in the clubhouse on 67, with Dewi Claire Schreefel of the Netherlands also at five-under through 10 holes.