While she has yet to win on the LPGA Tour, she has eight top-10 finishes this season for earnings of $864,000.
Thailand's Moriya Jutanugarn is two shots behind Park on 65, one shot ahead of Anna Nordqvist of Sweden and Katherine Kirk of Australia.
The only sisters to have won on the LPGA Tour are Annika and Charlotta Sorenstam.
"But I reckon if I keep knocking on the door, one day it will be my turn", she said.
Thailand's Moriya Jutanugarn will be seeking to join her younger sister Ariya in the golf majors record book as the first sisters to both win majorsDefending champion In Gee Chun of South Korea, whose 21-under total then set a majors record, shot a second straight 70 to be 2 under.
Ariya has missed the cut in three consecutive majors.
Last month, Jutanugarn was in second place and in the final Sunday pairing at the Ricoh Women's British Open at Kingsbarns.
Former No 1 Lydia Ko of New Zealand, the 2015 Evian victor, and Ayako Uehara of Japan each picked up three shots to be 6 under.
She's in position to do that well, or better today.
On six-under, just three off the lead, are a formidable threesome. Two holes later, play was stopped.
But on a leaderboard unusually bound by Thursday's vile weather at Evian Les Bains in France causing a round to be wiped and the tournament to be played over 54 holes, Aussie eyes will fall on Kirk.
"I was lucky", admitted the 23-year-old South Korean. "I just keep trying".
"I mean, golf is amusing; I wasn't expecting it for sure, but yeah, I kind of surprised myself even, and certainly since then, it's just, yeah, been nice".
Park said: "I didn't play well today, so I have a little gap from the top players. Putted well and I am delighted with the score".
But Mel Reid mixed four bogeys with two birdies in a 74 which saw her slide to one over, while Charley Hull will also be playing for pride in the final round after failing to build on a bright start to her 69.
Ariya Jutanugarn became the first Thai golfer to win a major at last year's Women's British Open, and victory for her older sibling on Sunday would make them the first sisters to be major champions since the formation of the LPGA Tour in 1950.
"That (win) was a huge confidence boost, especially after struggling for a couple years and questioning whether I'd be playing much longer", Kirk confessed after her second-round 69.