World number two Jin Young Ko piled up nine birdies to take a three-shot lead at the Cognizant Founders Cup in West Caldwell, NJ, while Stephanie Meadow and Leona Maguire both struggled to keep pace.
With her 8-under 63, Ko extended her streak of rounds in the 60s to 11 - the third-longest run in LPGA Tour history and only three shy of tying Annika Sorenstam's record.
Ko said that record was not on her radar.
"If I can, even, it's going to be great honor," Ko said.
Ko hit 15 greens in regulation and needed just 25 putts to leap ahead of the pack at Mountain Ridge Country Club, which is hosting the event for the first time. Ko won the cup in 2019 at Wildfire Golf Club in Phoenix.
By contrast Irish duo Maguire and Meadow had a testing day, with Maguire looking to be in danger of missing the cut already.
Solheim Cup star Maguire will be disappointed with her round of 74 which included five bogeys and just one birdie and leaves her on +4.
Meadow fared better and sits in the clubhouse on -1, but will have to return early on Friday morning to complete her round as she still had three holes to complete when darkness fell.
Germany's Sandra Gal took second place with her bogey-free, 5-under 66. Starting on the back nine, Gal birdied three of her first five holes and later carded twos on the par-3 fifth and seventh holes. She left her tee shot at No.7 just a foot or two away from the cup.
"I came into the tournament striking it really nicely and it's kind of been building up the last few weeks, but until you see the results on the course you just got to play, play, play," Gal said.
Gal has just one LPGA Tour win to her name, and it came 10 years ago at the2011 Kia Classic.
A six-way tie for third at 4-under 67 includes world No. 1 Nelly Korda, playing for the first time after taking three weeks off to rest a slight shoulder injury. Korda potted six birdies with two bogeys; at one point Thursday, she shared the lead with Ko at 5 under before slipping back.
"It was good. Felt nice to kind of get the juices flowing again," Korda said."Yeah, not complaining about today. There is some stuff that I can work on, but not complaining.
"You don't win it on Day 1, but you can definitely lose it," she added. "Just trying to stay consistent and play my golf and get some opportunities where Ican sink some putts."
Tied with Korda at 4 under are fellow major winners Brooke Henderson of Canada, So Yeon Ryu of South Korea and Yuka Saso of the Philippines. Also in that group are France's Perrine Delacour, last week's winner in South Jersey, and South Korea's Amy Yang.