The form of the world number two golfer, Lydia Ko, has been solid but not spectacular after three rounds of the Portland Classic.
Following rounds of 70, 72 and 72, Ko is two under for the tournament, in a tie for 53rd, 16 strokes behind the run-away leader.
Brooke Henderson could become the third player in LPGA history to win a tour event before turning 18, after opening a five-stroke lead.
The 17-year-old Canadian fired a bogey-free seven-under 65 in the third round at Columbia Edgewater Country Club in Oregon to run away with the lead.
She was at 18-under 198 with one round left, while American Morgan Pressel also shot 65 to move into second place on 13-under.
"I know it's long from over and there's a lot of great players behind me," Henderson told reporters.
"I saw a nine-under (score) on the board and a couple seven-unders, so it's definitely doable on this golf course. I know I'll have to put a solid round in."
If Henderson closes the deal on Sunday she will join Ko and the American Lexi Thompson as LPGA winners before their 18th birthday.
Ko was 15 when she first won, while Thompson was 16.
Henderson had the 54-hole lead at the Swinging Skirts Classic in San Francisco earlier this year, but finished third, one shot out of a playoff between Ko and Pressel that was won by Ko.
In nine LPGA events this season, Henderson has three top-five showings, including equal fifth at both the KPMG Women's PGA Championship and U.S. Women's Open.
A Henderson victory would also end a long Canadian drought.
Nobody from her homeland has won an LPGA tournament since Lorie Kane claimed the Takefuji Classic in Hawaii in February 2001.