World number two Ko Jin-young surged to the top of the leaderboard on Friday with a five-under 67 to take a one-shot lead at the halfway stage of the LPGA Portland Classic.
Ko, who is playing in her first tournament since failing to win a medal at the Tokyo Olympics, rolled in six birdies, including back-to-back efforts at the 13th and 14th, with the only blemish a bogey on the par-four 11th.
Ko finished a disappointing ninth at the Games in Japan six weeks ago then took a break at home in neighbouring South Korea to spend time with family and friends.
"I am playing really good right now," she said. "I spent over a month in Korea, so I feel really fresh."
Scotland's Gemma Dryburgh is alone in second after shooting a 69 in Friday's second round at the Oregon Golf Club.
First round co-leader Carlota Ciganda of Spain fired a 71 and is in solo third, three strokes behind Ko.
Ko needed just 48 putts in her first two rounds and says the greens at the course are in great condition.
"If I putt as I see the green, I have the confidence that they will always go in," she said.
Ko played in a group with long-hitters Patty Tavatanakit of Thailand and American Angel Yin.
Tavatanakit, who won her first major at the ANA Inspiration this year, is one of the longest drivers on the tour.
The 21-year-old from Bangkok bounced back with a five-under 67 to be tied 14th after carding a disappointing four-over 76 in Thursday's first round. Yin shot a 74 and is tied for 23rd, nine shots behind Ko.
"They hit so far, so I try to not look at the swing or distance," Ko said. "But Patty played good, so I wanted to follow her. That's why I play really good today."
Dryburgh, who won her first LPGA title at the World Invitational in Northern Ireland last month, drained three consecutive birdies, beginning at the par-four 16.