The 32-year-old won her third LPGA title and first since capturing the 2017 Women's Scottish Open after firing a one-over 73 on Sunday to finish with an 11-under total of 277 at the Jian Lake Blue Bay Golf Course.
She finished one stroke better than China's Weiwei Zhang (69 on Sunday), who failed to hold the lead after a bogey on the 17th hole.
"Still kind of a little bit shake my hands," Lee said of her nerves.
"First hole make birdie, but like two double front nine and then finish four-over so was almost give up, but my caddie just kept telling me keep fighting, fighting.
"I really fought by myself, just didn't give up, and then I just got to make a lot of birdies, so I think amazing. Feels amazing, yes."
Lee became only the second South Korean to win the Blue Bay LPGA, joining 2015 champion Sei Young Kim
Auston Kim (71) made three birdies over the final five holes to reside in a third-place tie with Aditi Ashok (72) of India.
Australia's lone entrant Robyn Choi finished with a disappointing 76 to end on one-over for the tournament, tied for 24th place.
