Kupcho fired an eight-under 64 that included nine birdies and one bogey to move clear at the top of the standings with one round to go.

The world number 54 registered birdies at eight of the first 12 holes including three in succession to move in front.

A bogey at the par-four 13th was the only blip in her round as she recovered to score another birdie at the par-three 17th to establish a commanding lead.

"Everything was working," said Kupcho.

"I putted really well, and you have got to make putts in a major championship.

"I can't control what anyone else is doing.

"Someone else can go out and do what I did today, so I have really just got to go out and focus on hitting the fairways and greens and putting good strokes on putts."

Kupcho’s closet rival is defending champion Patty Tavatanakit of Thailand who is six shots back going into tomorrow’s final round.

Tavatanakit followed rounds of 67 and 69 with a two-under 70 as she looks to become only the second player in history to defend the title, last achieved by Sweden’s Annika Sörenstam, the head of the International Golf Federation.

"I like chasing," said Tavatanakit.

"You play without fear and I love doing that."

American Jessica Korda posted a five-under 67 to climb to third on nine under courtesy of six birdies and one bogey today.

Annie Park of the US sits in fourth place on seven under after a one-over 73, while six players are tied fifth on six under.

Japan’s Hinako Shibuno held a one-shot lead overnight after rounds of 69 and 66 but has slipped to 21st position on four under following a five-over 77.

Competition is due to conclude tomorrow.