Defending champion Lexi Thompson fired a nine-under par 63, matching the course record to grab a two-stroke lead after the first round of the Navistar LPGA Classic.
The 17-year-old American won the event by five strokes last year, becoming the youngest champion in LPGA history at age 16 -- a mark broken by 15-year-old New Zealand amateur Lydia Ko at last month's Canadian Women's Open.
But Thompson showed no sign of being surpassed at the Robert Trent Jones Golf Trail's Senator course, firing nine birdies without a bogey to finish the round two strokes ahead of American Lizette Salas and South Korean Hee Young Park.
"It feels really good getting a first round of 63 under my belt, but you just have to take it one shot at a time," Thompson said. "I hope to play like I did for the next three rounds."
Thompson opened her career-low round with a birdie, then ran off three in a row starting at the par-4 fourth.
She closed the front nine and opened the back nine with birdies, added another birdie at the par-3 13th, and also had back-to-back birdies at the par-3 16th and par-5 17th.
At the 18th, with a chance to claim the course record all for herself, Thompson missed a birdie putt by six inches.
"I wasn't thinking about the course record," she said. "I was just trying to put a good stroke on it like every other putt."
Thompson, ranked 25th, missed only one green in regulation in matching the course record of 63 set by Japan's Mika Miyazato and Australian Lindsey Wright in the 2010 event.
Thompson, whose previous career-low round was a 65 fired at the Navistar in 2009, had a specially prepared breakfast at her favorite grill-to-order diner near the course as she did before her rounds last year before her only LPGA title. She dined on egg whites, bacon, wheat toast and potatoes.
"Valerie (Perry), she's the main cook there and she sings, so it keeps me relaxed, keeps me laughing before my round," Thompson said. "It's a good atmosphere."
Britain's Karen Stupples, South Korean Mi Hyang Lee and Americans Amanda Blumenhurst, Wendy Ward and World No. 2 Stacy Lewis, seeking her third title of the year, shared fourth on 66.
"It was actually a pretty frustrating 66," Lewis said. "I had a ton of putts go right over the edge and just lip out."
On 67 were Canada's Lorie Kane and Alena Sharp, and Americans Sydnee Michaels, Angela Stanford, Dori Carter and Karlin Beck.
World No. 1 Yani Tseng of Taiwan opened with a 71.