Lee had a 5-under 214 after three rounds, a stroke ahead of Americans Alison Walshe (69) and Beth Allen (73).
Webb, who is attempting to win a her fifth Open overall, is in a four-way tie for fourth with Choi He-young of South Korea (71), Australian Emma Bennett (73) and Tania Elosegui of Spain (75) at 4-over 216.
I need to not make as many mental mistakes as I did today, Webb said. If I can do that Ill have a good chance.
Lee slumped through the middle holes at the Metropolitan Golf Club with four straight bogeys before regaining her composure.
I was very nervous and stressed and I couldnt think clearly, Lee said through an interpreter. Then I saw the leaderboard and saw I was on top so I felt relieved and got back into my game.
Laura Davies of Britain, who won the Australian Open in 2004, was the biggest mover Saturday, shooting 67 for the best round of the day and, at 2-under 217, the veteran is three shots back.
Davies was in a five-way tie for eighth that included American Diana DAlessio, who shot 69 Saturday.
The conditions were perfect and I had a couple of pretty good stretches, Davies said.
Her best stretch came when she was 4-under in three holes ' a birdie on the par-3 13th, another on the par-5 14th and an eagle on the par-5 15th. Davies also had three birdies in a row on the front nine.
Australian Katherine Hull, an LPGA regular who won last weeks Australian Masters at Royal Pines, shot 70 Saturday and is tied for 26th, six strokes back.
Walshe, a former star amateur, is playing in only her second pro event after cashing a check at last weeks Masters.
The 23-year-old Walshe, born in Galway, Ireland, but raised Westford, Massachusetts, said she didnt expect to be leading the tournament late in her round Saturday.
I saw it for the first time on 16 and I was surprised, Walshe said. It was not too windy on the front nine and I was surprised that a lot of the other players had not scored well on the back. I hope I can hang on.
Walshe played in Adelaide, Australia, last October in the Espirito Santo womens amateur teams event, leading the United States to a third-place finish. She was also on the winning Curtis Cup team over Britain and Ireland last June at St. Andrews, winning all three of her matches.
You always want to win and its definitely what I will be shooting for, she said. But I dont want to get ahead of myself and shoot myself out of it.