Kim Kaufman thrust herself into contention for a first ever victory after firing a superb eight-under-par 64 to grab a share of the lead at the LPGA Tour Championship on Saturday.
The 26-year-old world number 114 produced a flawless display at the Tiburon Golf Club in Naples, Florida, comprising eight birdies and 10 pars to surge up the leaderboard.
Kaufman's dazzling round gave her a 54-hole aggregate of 206, putting her in a four-way tie for the lead at 10 under.
However Kaufman, whose best performance this year was a share of sixth place at the Marathon Classic in July, can expect a strong challenge on Sunday from her rivals.
Michelle Wie, Thailand's Ariya Jutanugarn and Norway's Suzann Pettersen are also on 10 under heading into the final round.
Wie, who only recently returned after a two-month layoff following an emergency appendectomy, made her move with a six-under-par 66 featuring seven birdies and one bogey.
Wie said afterwards she was finally starting to feel fully recovered after returning to play last month.
"I really did struggle for a bit just really trying to get my feel back, but every week was an improvement," said Wie.
"Every week I felt like I got a little part of my game back. From last week I felt pretty good. I'm just excited to end the season on a good note."
Thailand's Ariya meanwhile had a bogey-free five-under-par 67.
However there was disappointment for second round leader Park Sung-Hyun, who had started the day three shots clear of the field.
Park, who is chasing a win this weekend which could give her Player of the Year honours as well as the $1 million playoff bonus, struggled to a three-over-par 75.
The 24-year-old US Women's Open champion remains firmly in contention though on Sunday, just one off the lead on nine under.
Park's problems began on the front nine, with a bogey on the second which was followed by a double-bogey seven on the par-five sixth.
She looked to have steadied the ship with back-to-back birdies on the 13th and 14th to edge into a one-shot lead.
But a brace of bogeys on the run-in saw her drop back into the chasing pack.
"I think the tee shots were not quite solid, so there was something missing out there," Park said. "Over the course of four days there is always a day when you are not in top shape and that was today.
"Keeping your focus all four days is difficult. The key is how you cover up your loss of focus. There are a lot of top players on the leaderboard. The key tomorrow will be keeping my focus."
Park is tied with six others on nine under, a group that includes Stacy Lewis, Austin Ernst, Lexi Thompson, Jessica Korda, Sweden's Pernilla Lindberg and France's Karine Icher.
China's world number one Feng Shanshan posted her best round of the tournament with a five-under-par 67, leaving her four off the pace at six under.