Lydia Ko's chances of winning a third straight Swinging Skirts Classic tournament are slim going into today's final round of the LPGA Tour event in California.

Ko shot a 73 in the penultimate round which left her tied for eighth and six shots off the lead, held by Japan's Haru Nomura, who shot a 71 to reach a 10-under 206.

But New Zealand's two-time major champion hasn't given up hope of victory on her 19th birthday today.

"My game wasn't really up to it," said Ko of her third round. "It was pretty average. But I felt like chipping, short game-wise, it was good.

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"I wasn't making the putts that needed to go in for birdie or those crucial par saves ... I've just got to stay positive."

Nomura met rules officials after the round to discuss her play from an awkward stance in the left greenside bunker on the par-5 sixth hole.

"It was slopey, so I was trying to take a stance, but I kept slipping downhill, and in order to get a firm stance, I had to - even when I had to do a practice swing - I had to swing real hard, and when I did, I kept moving forward again and again," Nomura said.

"There was no option but to move like that, but they were saying that I was moving excessively, but what I was trying to tell them was, 'OK, then what is the guideline?' There should be some sort of a standard, a regulation that explains what an infraction is and not."

The officials decided no penalty was warranted, leaving her with a par on the hole.

"For me, the two-stroke penalty, it wouldn't really have made a big difference," Nomura said. "If I did something wrong, I have to accept it."

Australian teen star Minjee Lee's hopes of a second consecutive LPGA Tour title slipped in a tough third round at the Swinging Skirts Classic. She battled to a two-over 74 to sit alongside Ko on the Lake Merced course where she won the US Girls' Championship four years ago.

South Africa's Lee-Anne Pace (69) and South Korea's Na Yeon Choi (71) were tied for second. Choi won twice last year and has nine LPGA Tour victories.

"It was tough," Choi said. "I think especially the greens were so firm and a lot of holes have front pins, so it's hard to stop the ball around the pin. I like chasing, so I feel great about this tournament and this week and about my game."

- AAP