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
