"Yeah, it was a really good round," Ko said. "I made a couple of silly mistakes like making a bogey on eight, which was a par five. Most of the time you make a birdie, then a bogey, so I was a little upset about that but then I kind of finished it well with another birdie and that."
The Victorian course allowed plenty of players to get under the card. Hee Young Park, Marion Ricordeau and Americans Jessica Korde and Jaclyn Sweeney were tied for second at five-under, one stroke back from Pettersen and a shot ahead of Ko.
"It's definitely not easy," Ko said of the course. "I came here with a goal, maybe three under par and I shot better, so that's great. But you know, seeing Suzann up top and then she had an amazing round, it can get really tough, especially with the wind getting higher."
After attracting a huge gallery during the New Zealand Women's Open at Clearwater two weeks ago where she finished second, Ko said there was less pressure playing in Australia.
"I think it's actually the opposite, you know, I feel so relaxed here. I play such good golf over here and everyone's supporting me, so I feel really relaxed. I think I'm more pressured when I'm home/home in New Zealand but it's always great to come out here and play in Australia."
This week's tournament is Ko's third for the year after she opened 2014 with a seventh place finish at the Bahamas LPGA Classic last month before she fell just short of defending her New Zealand Women's Open crown at Clearwater.
Pettersen believes she has the brawn and brains to win the title.
After her round, a confident Pettersen was asked about a drive on the 13th that travelled about 280m.
"Have you not see my guns?," she asked, flexing for the assembled media.
The gym work has paid off with a faster swing and more energy as she tries to better four LPGA victories.
- APNZ, AAP
