Los Angeles - Kim Sei-Young, seeking her second win of the season, shared the first-round lead at the Thornberry Creek LPGA Classic with Belgian rookie Laura Gonzalez Escallon on Thursday in Oneida, Wisconsin.
South Korea's Kim, whose season has included a win at the Lorena Ochoa Match Play and three more top-five finishes, had eight birdies and a bogey in her seven-under 65 while Escallon had seven birdies without a bogey.
"It's been a long time since I played well in the first round, so I'm very blessed to have shot a seven-under," Kim said. "My shots were solid today and the greens were softer so I was able to go after the pins and give myself a lot of birdie opportunities.
"And then putting was good, and I made a lot of birdies."
Although she's seeking her first LPGA title, Escallon has been impressive in her rookie season. She notched a top-10 finish in her debut, and had was tied for fifth at the Manulife LPGA Classic last month.
"I started with a top 10, so that was a dream come true, and I mean, I'm just learning and enjoying it here," Escallon said. "I have a great caddie... so that helps just to have fun and enjoy it and try to meet people and get to know the courses."
Escallon birdied three of her first four holes, then came alive again with three straight birdies at 14, 15 and 16 before capping her round with another birdie.
"I started really hot and then I kind of stumbled a little bit, so my goal was to finish strong, and I did that," she said.
Kim and Escallon were one stroke in front of American Madeleine Sheils and South Korean Kim Min-G. Both rookies had six birdies without a bogey.
It was a further stroke back for a group of 17 players on 67 that included South Korea's world number five Chun In-Gee, who is seeking her first win of 2017, France's Karine Icher and Thailand's Moriya Jutanugarn.
Another 14 golfers were a further shot back on four-under 68 including England's Charley Hull, Norway's Suzann Pettersen and Germany's Sandra Gal.
With 35 golfers separated by three shots at the top of the jammed leaderboard, Friday's second round promised to be a scramble for position heading into the weekend.
World number two Ariya Jutanugarn, the highest-ranked player in the field, looked unlikely to make it past Friday.
She had five bogeys and a double bogey with just one birdie in a six-over 78 that left her languishing at 142nd in the 144-woman field.
Leading first-round scores on Thursday in the Thornberry Creek LPGA Classic at Oneida, Wisconsin (USA unless noted):
65 - Kim Sei-Young (KOR), Laura Gonzalez Escallon (BEL)
66 - Madeleine Sheils, Kim Min-G (KOR)
67 - Caroline Hedwall (SWE), Rachel Rohanna, Bronte Law (ENG), Karine Icher (FRA), Moriya Jutanugarn (THA), Pornanong Phatlum (THA), Lee Il-Hee (KOR), Dani Holmqvist (SWE), Amelia Lewis, Brooke Pancake, Alejandra Llaneza (MEX), Samantha Troyanovich, Brittany Altomare, Chun In-Gee (KOR), Alena Sharp (CAN), Katie Burnett, Pavarisa Yoktuan (THA)