- In-Gee Chun shoots six-under 65
- Leads final major by four shots
A double bogey on the ninth was the only blemish on Chun's otherwise perfect scorecard Saturday, and the 22-year-old now has her eye on the all-time lowest score recorded at a women's major.
She is chasing the 19-under-par total shot by Karen Stupples at the 2004 British Open, which was matched by Inbee Park
at the PGA Championship in 2015.
"It's a really big honor for me," Chun said of equaling the feat. "But I just have to stick with my game plan.
"The game plan for tomorrow is just to keep doing the same thing.
"I'm not going to think about winning. I just want to keep enjoying what I am doing."
Fellow South Korean Sung Hyun Park was four shots back on 15 under par, but was still confident of closing the gap.
Her last professional win, which came on the Korean Tour, was also from four shots behind.
"I know I need to shoot low tomorrow," she told reporters after her round. "I have known In-Gee since we were at elementary school. We are good friends."
This is Chun's first year on LPGA Tour and she is aiming to become only the second woman in history to win her first two LPGA titles at major championships, following in the footsteps of compatriot Se Ri Pak.
Chun's first major victory came in last year's US Open, although she failed to make the cut in the defense of her title
Chinese golfer, and bronze medalist from Rio 2016
, Shanshan Feng was a further two shots back and alone in third place.
Reigning champion Lydia Ko
had an afternoon to forget, with New Zealand's world No. 1 shooting a four-over 75 to be tied for 34th.