Lydia Ko in control at LPGA Tour tourney

Lydia Ko is in total control of the CME Group Tour Championship and halfway there on picking up the coveted player-of-the-year gong.

She is also in total control of the season-long scoring and money races, too.

Ko shot a 6-under 66 in Friday's second round of the LPGA Tour's season finale, pushing her to 13 under for the tournament and five shots clear of Hyo Joo Kim through 36 holes.

Ko made four birdies in a six-hole stretch midway through her round, rolled in a testy 4-footer to save par on the par-4 13th to maintain what was then a four-shot lead, and hasn't dropped a shot since her opening hole on Thursday.

"I just wanted to focus on my game," said Ko, who turned a one-shot lead entering Friday to a five-shot edge when it was over.

"It was a pretty tight leaderboard. I shot a low one yesterday and that round, it can be anybody throughout the week."

Except right now, nobody else is going as low as Ko.

Ko's 66 was the round of the day with four others shooting 67s. Through two rounds at Tiburon, there have been four scores of 66 or lower; Ko has two of them after an opening 65.

Kim (69) made back-to-back birdies on 16 and 17 to get to 8 under, alone in second.

World No.1 Nelly Korda (69) is in a pack tied for third at 7 under, along with Japan's Nasa Hataoka (67), Sweden's Anna Nordqvist (69) and Scotland's Gemma Dryburgh (70).

Korda was making a move on the front, closing her first nine with three birdies in a four-hole stretch. But she made nothing but pars on the back nine.

"Lyds is playing well. She's had an amazing year," Korda said. "To catch her I'm just going to have to play aggressive and drain the putts."

And even that might not be enough. Everyone is chasing Ko, who is chasing trophies and more.

Ko entered the week with a one-point lead in the race for LPGA Tour player of the year. She needs to avoid just all-out disaster on the weekend to win her second consecutive Vare Trophy for having the year's lowest scoring average. Those titles would move her closer to the LPGA Hall of Fame.

And with $US2 million ($A3 million), the biggest single prize in women's golf, awaiting the winner that means the money title is within her reach as well.

"It was a solid day," Ko said. "It was more solid than yesterday. ... I couldn't really have asked for more to start this week."

Ko is now averaging 68.964 this year. Atthaya Thitikul's average for the season is now 69.447. It would take about a 40-shot swing between them on the weekend for Thitikul to catch Ko in that race.

And if Ko wins the tournament, she'd push her earnings for 2022 to $US4,364 million ($A6.5m) and virtually lock up the money title as well.

Australia's Minjee Lee, who is only a point behind Ko for the best player gong, shot a 68 to follow her 71.

Lee is tied 10th with her 6-under total and is eight behind runaway leader Ko.