South Korea's Lee So-mi fired an eight-under par 64 to seize a two-stroke lead over American Allisen Corpuz after Thursday's opening round of the LPGA Tour Championship.
Lee birdied seven of the first 15 holes and eagled the par-five 17th before a closing bogey at Tiburon Golf Club in Naples, Florida.
"My tee shot and putter were the things I was focusing on and I really practiced them a lot. I think that was the foundation to my success today," Lee said through a translator.
The $11 million event features 60 players who qualified during the season chasing the LPGA's biggest prize of $4 million.
Top-ranked defending champion Jeeno Thitikul of Thailand shared third on 67 with Japan's Nasa Hataoka and South Koreans Kim Sei-young and Im Jin-hee.
World number 50 Lee, a 26-year-old from Wando, won her first LPGA title in June at the Dow Championship pairs event alongside Im and shook off the nerves of her first Tour Championship.
"It's an honour playing my first Tour Championship and I don't think I was necessarily in a position to be nervous about anything," Lee said.
"I thought to myself, whatever the score is or how I play, let's just prepare for next year's season. I think that kind of alleviated the stress in today's round to be able to get a better score."
Lee made back-to-back birdies at the third and fourth holes and again to close the front nine. She birdied 11 and another two in a row at the par-five 14th and par-four 15th before her eagle-bogey close.
"Mind control is probably the most important factor going into the remaining rounds," Lee said.
"I wanted to play 18 better. Whether my golf game is good or bad I know that's not the end of my golf career, so I want to do my best."
Corpuz answered her lone bogey at the third hole with birdies on the next four, another to begin the back nine and two more at the par-three 16th and par-five 17th.
"I was really just always in play. Had a lot of birdie looks. Converted a few of them," Corpuz said.
"It feels like I've been playing really well recently, just haven't quite scored. It was nice to get it all out there."
Jeeno had three birdies on both the front and back nine with a bogey at the ninth to stay in the hunt for the title.
"I know we're playing for $4 million, but to me I think it's just like almost a bonus for me this year to be able to play here," Jeeno said.
Jeeno, seeking her third title of the season, is also in the hunt for the season money crown, the Vare Trophy for low season scoring average and the LPGA Player of the Year award.
World No 4 Minjee Lee of Australia leads the season prize money list with $3 822 388 while Jeeno sits $244 058 behind.
Jeeno leads in scoring average for the season on 68.88 strokes with world No 2 Nelly Korda of the United States second on 69.58.
Jeeno leads in the Player of the Year chase by 16 points over Japan's third-ranked Miyu Yamashita, who has already clinched the LPGA Rookie of the Year award.