(Reuters) - LPGA rookie Jang Ha-na took advantage of a late wobble by world number one Lydia Ko to grab a two-shot lead after the second round of the season-ending CME Group Tour Championship in Naples, Florida on Friday.
South Korean Jang, hunting her first title on the U.S. circuit after ending up second three times this year, birdied four of her first six holes before finishing birdie-birdie for a seven-under-par 65 at Tiburon Golf Club.
That left Jang at 10-under 134, two ahead of New Zealand teenager Ko who carded a 67 that was highlighted by eight birdies but damaged by a double-bogey at the par-four 15th and a bogey at the par-three 16th.
Twice major winner Cristie Kerr and fellow American Jennifer Song were a further stroke back at seven under after posting matching 69s.
For the fifth time in her rookie season, Jang holds the 36-hole lead but she does not want to look too far ahead.
"In the Marathon Classic, I played a playoff with Chella Choi ... I thought too much that I want to be champion," Jang, who is ranked 15th in the world and a six-times winner on the Korean LPGA Tour, told reporters.
"So I don't want to think about being leader."
Though Ko stumbled over the closing stretch, she maintained her grip in the race with Korean Park In-bee for 2015 LPGA Tour honours as she seeks her sixth victory of the season.
Ko is in pole position to clinch the LPGA Player of the Year award, the money list title and retain her number one ranking, while Park has a slight edge in the chase for the coveted Vare Trophy for best scoring average.
"It's right there," said Ko, who would clinch The Race To The CME Globe, which carries a $1 million bonus, with victory this week where the winner's check is for $500,000.
"My trainer and I always say, 'Hey, better every day.' It's what I try and work towards, too. If I keep getting better every day, it ends up being a few low scores."
Ko, who won last year's CME Group Tour Championship in a three-way playoff to land 2014 LPGA Rookie of the Year honours, shrugged off her double at the 15th where she hit a tree with her second shot.
"I played a little too cute," she said. "I should have taken my medicine."
Park, a winner of two major championships this year, returned a 69 to end the second round six strokes off the pace.
American Austin Ernst, who held a one-shot lead overnight after opening with a 66, triple-bogeyed the par-five first on the way to a roller-coaster 73 and a five-under total of 139.
(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Larry Fine)