Lee, who turns 22 on Sunday, held a two-stroke heading into the final round at Ann Arbor, Michigan.
She's been knocking on the door all season, with her five top-10 LPGA finishes including a playoff loss to Lydia Ko in San Francisco in April.
Lee nabbed her fourth birdie of the day at Travis Pointe's par-five 18th to build a 12-under par total of 204.
Last week's Volvik Championship winner Ariya Jutanugarn shot a 70 for a total 8 under, four off the pace.
American Stacy Lewis, expecting her first child later this year, fired a 67 to join a group sharing second on 206. She was joined by South Korea's Kim In-kyung, who also posted a 67, and by England's Jodi Ewart Shadoff and American Lindy Duncan, who both signed for 69s.
"I had a pretty solid day today, made no bogeys," said Lee, who is seeking a fourth LPGA title and her first since 2016. She finished second in this event by a stroke last year.
Although play was halted for more than two hours by rain, Lee said the greens firmed up by the time she finished her round.
"I think just keeping it in play was pretty important today," she said.
Ariya Jutanugarn of Thailand
Lewis, seeking her first win since the Portland Classic last August, said she didn't hit the ball well, but made some solid up-and-downs to get on a "nice little run."
"This golf course, you can shoot a number," said Lewis, who birdied four of her last five holes. "You can shoot six- or seven-under, but you can also play pretty good and shoot even par.
"So you've just got to get runs like I did there at the end of the day and just keep hanging around and post a number and see what happens."
Lewis admitted she was tired after the stop-and-start day, but said she didn't think her pregnancy prevented her from being competitive.
"The little one was telling me it's dinner time right now, but other than that I feel pretty good," she said. "Excited to be in the hunt."
Japanese 19-year-old Nasa Hataoka, who held a one-stroke overnight lead over Lee, made a promising start with a birdie at the second, then had five bogeys before back-to-back birdies at 14 and 15 to post a two-over 74.
That left her tied for 15th, five shots off the pace.
Published : May 27, 2018
By : AFP