Canada's Brooke Henderson is on course to becoming only the third player in LPGA history to win a tour event before turning 18, after opening a five-stroke lead at the Portland Classic.
The 17-year-old hit a seven-under 65 in the third round at the Columbia Edgewater Country Club in Oregon.
She also equalled the tournament's 54-hole record of 18-under 198.
Lydia Ko and Lexi Thompson are the only players to win an LPGA Tour title before their 18th birthday.
"I had a lot of fun out there today," said Henderson, who reached the tournament via the qualifiers on Monday.
"I got some lucky breaks. I think that's due to my positive energy. I try to focus on my shots and block out any negativity."
American Morgan Pressel also hit a 65 on Saturday to move second on 203, one stroke ahead of German pair Sandra Gal and Caroline Masson with one round remaining.
A win on Sunday will give Henderson an LPGA Tour card for next season.