New Zealand’s Lydia Ko finished round one of the CME Group Tour Championship at a one-point lead for the LPGA Tour player of the year at Naples in Florida.
After starting the week at the top of the CME Globe rankings, the 25-year-old ended on seven-under 65 in her bid to win the $2m (£1.6m) prize.
The day started with her hitting a tree and making bogey on a par five before making eight birdies, including four in a row late in the round at Tiburon Golf Club.
Ko is also in a lock to win the Vare Trophy for the lowest scoring average.
Danielle Kang and Pajaree Anannarukarn of Thailand were at 66, Gemma Dryburgh of Scotland and Hyo Joo Kim of South Korea were at 67 and the group at 68 included Nelly Korda and Brooke Henderson.
While Jin Young Ko of South Korea opened with a 72 as she continues to deal with an ailing left wrist.
Australian Minjee Lee, who already has set an LPGA Tour record with 3.7 million dollars (£3.1million) in earnings this season, opened with a 71.
Atthaya Thitikul of Thailand, the 19-year-old who reached No 1 in the world until Korda took it back, had a 73.
Korda had a chance at all the awards last year until Jin Young Ko beat her, making it the third straight year the South Korean star had won at Tiburon.
