Japanese rookie Akie Iwai fired an eight-under par 64 to seize a two-stroke lead after Saturday's third round of the LPGA Portland Classic.
The 23-year-old from Saitama, seeking her first LPGA victory, made seven birdies and an eagle against a lone bogey to stand on 18-under 198 after 54 holes at Edgewater Country Club.
Australia's Grace Kim, who captured her first major title at the Evian Championship, made a stunning eagle at the 17th, holing out from 156 yards from the fairway rough to shoot 67 and grab second on 200.
World number 29 Iwai, an LPGA runner-up this year at Thailand and the LA Championship, has won six times on the Japan Tour.
"After I made the eagle at five, I had many birdie chances, so good tempo," Iwai said.
"My style is aggressive. No change this week. Aim to the pin. Every shot. Every hole."
That was apparent at the 18th hole, where she dropped her approaches inches from the hole and tapped in for her fourth birdie on the back nine.
After answering a bogey at the par-three second hole with a birdie at the third, Iwai eagled the par-five fifth followed by back-to-back birdies at six and the par-five seventh.
She began the back nine with birdies at the par-five 10th and 12th holes and added another at the par-three 13th to reach 17-under and lead by three strokes.
Kim went four-under over the last five holes to charge into the second with birdies at 14 and 15 and her eagle at 17 the shot of the round.
She looked away after the ball landed in the rough, not seeing it bounce onto the green, roll down a slope and into the hole for an eagle.
"I leaked my driver a little right," Kim said. "I thought I was going to be in the rough, which it was, and I was trying to see if I could get a drop. I wasn't entirely over the sprinkler head boxes so I knew I just had to hit it.
"It leaked right again and I was like, 'Oh please get through the rough,' and somehow it went in the hole so I guess it's a little bit of luck in there."
Sweden's Linn Grant took third on 202 with a 65, one stroke ahead of American Gurleen Kaur with India's Aditi Ashok and American Gina Kim on 204.
"I had a good round out there," Grant said. "Tried to go out and just be, I wouldn't say happy, but just accepting of whatever today would bring. I played very mature and just had a lot of fun."
South Korea's Lee5 Jeong-eun led after 36 holes but made a triple bogey at the par-four sixth hole to fall eight off the pace.