Lee started the day a shot behind overnight leader Brittany Lang with Cristie Kerr and South Korean number one Park Sung-hyun in hot pursuit two strokes further back.
However, all three of her rivals failed to break par on Saturday, with Lang and Kerr carding matching 72s and Park slumping to a one-over 73 after back-to-back double bogeys at the 14th and 15th left her seven shots off the pace.
Lee missed a short putt on the third hole but hit back straight away with four consecutive birdies. Another bogey at 14 was followed by birdies at 15 and 18.
"On number three I missed like a three-footer for par. I three-putted and that kind of spooked me a bit," she told reporters.
"When I make a bogey, especially through a mistake, it kind of gets me a little angry ... and gets me more focused.
"So, yeah, I think the bogey almost helped because it kind of snapped me back into the game and got me more focused."
Despite her cushion, the 21-year-old said there was still work to be done to secure the title.
"I do have a few strokes ahead of the field; I feel like there are a lot of birdies out there you can get, and a lot bogeys as well if you get in the wrong spot."
(Editing by Ed Osmond)
