With brother Curtis back at her side at Tiburon Golf Club, Lexi Thompson shot a seven-under 65 on Thursday to take the first-round lead in the LPGA Tour's season finale in Naples.
Curtis, a Korn Ferry Tour player, also caddied for his sister in 2018 when she won the season-ending event.
"If we're both home we are always playing golf together and joking around," Thompson said.
"It's great to have him out here. I really appreciate him helping me out and keeping me loose out there. Whether I play good or bad, he always keeps a smile on my face."
On Thursday after early morning rain, Thompson birdied five of the first seven holes. She played the next nine holes in even par with a birdie and a bogey, then birdied the final two holes.
The 11-time LPGA Tour winner had her lowest score of the year a week after missing the cut in Houston in the US Women's Open.
"I was just overall very happy with how I committed to my shots," Thompson said.
"I've been working so hard on my game in general trying to improve on it, and it's been kind of an up and down roller coaster." – Lexi Thompson
"That's what I've really been working on. I've been working so hard on my game in general trying to improve on it, and it's been kind of an up and down roller coaster with an unfortunate week last week."
Nanna Koerstz Madsen of Denmark was a stroke back after a bogey-free round.
Defending champion Sei Young Kim was at 67 with Caroline Masson and Megan Khang.
Masson holed a 9-iron approach for eagle on the par-4 13th.
The Australian contingent made a solid start with five-time LPGA Tour winner Minjee Lee shooting a four-under 68 to lead the charge.
Just one behind the World No.8 is Hannah Green, the 2019 Women's PGA Championship winner.
Katherine Kirk and Sarah Kemp both shot even par to be in a tie for 36th.
The US$1.1 million (AU$1.4 million) winner's prize, down from US$1.5 million last year, is still the richest in women's golf.
Race to CME Globe leader Inbee Park and second-place Danielle Kang each shot 71, playing alongside Kim.
Kang led the points race since back-to-back wins in Ohio until Park took over the lead last week.