LOS ANGELES - World number one Lydia Ko fired six birdies in a five-under par 66 on Friday to grab a share of the lead in the LPGA Marathon Classic at the halfway mark alongside Kim Hyo-Joo.

South Korea's Kim, one of three players sharing the overnight lead, had four birdies in her three-under 68 to join Ko on eight-under 134 after two rounds on the Highland Meadows course in Sylvania, Ohio. Ko, who won the title here in 2014 for her second win as a professional, opened with a birdie at the 10th hole. A bogey at 11 was followed by birdies at 14 and 17, and she birdied three holes on her inward run.

"I started off well with a birdie on my first hole and then made a clumsy bogey on the next hole," Ko said. "I had a few birdies where it was three, four, five feet. When you've got those birdie chances, it makes it a whole lot easier."

She was pleased to have taken advantage of her chances, especially since the rising wind made things tougher on her last nine. "Number nine, I don't think I've ever come into that green with a six-iron," said the New Zealander, who barely got the ball on the green for a closing par.

Ko, whose back-to-back wins in California this year included her second major title at the ANA Inspiration, said her round wasn't much different from her opening 68.

"I think I had a few more looks for birdies and a few that decided to drop. Even today I had a few that were so close to going in and didn't drop, I felt like I did leave a few out there. "In this wind, I feel like my score is a pretty solid one."

She and Kim, who opened the season with a victory in the Bahamas, were one stroke in front of South Korea's Jang Ha-Na and American Alison Lee. Lee birdied her last two holes to cap a 66 while Jang signed for a 67 that included four birdies and no bogeys.

"Really good play today," said Jang, a two-time winner this season who said patience paid off. "Just target the middle of the green," she said. "Because this golf course has really small greens."

It was a further stroke back to Thailand's Ariya Jutanugarn (69), South Korea's Lee Mi-Rim (70) and American Lee Lopez (66). Brittany Lang, winner of the US Women's Open last week, carded a 69 that put her in a group sharing 16th place on 139.

World number two Brooke Henderson of Canada carded a one-over 72 that left her six shots off the pace while defending champion Chella Choi missed the cut after shooting a three-over par 74 that left her four-over for 36 holes.