'It's good because this is my first win on the LPGA Tour so I'm very happy,' said Lee, who pocketed $225,000 for the victory. 'Yeah, I'm very happy.'
Lee has already enjoyed a strong rookie campaign in 2006. She has runner-up finishes at the Fields Open in Hawaii, where she lost a playoff to Meena Lee, the MasterCard Classic and the LPGA Takefuji Classic.
She heads the race for the Louise Suggs Rolex Rookie of the Year award even though Lee became the third first-time winner this season. Joo Mi Kim and Sung Ah Yim both earned their maiden LPGA Tour victories earlier this year.
Defending champion Annika Sorenstam made some uncharacteristic mistakes on Sunday and never mounted a serious charge. She carded a four-under 67 and shared second place with reigning Women's British Open champion Jeong Jang (64) and Sherri Steinhauer (66). The trio came in at 13-under-par 200.
'I made a bunch of birdies and then finished with an eagle, but made a few mistakes out there early on,' said Sorenstam, who has only one win this season, but will try to defend her title next week at the LPGA Championship. 'It was not enough today.'
Sophie Gustafson flew out of the gate and held the lead for a period of time on Sunday. She pushed her drive at 18, then decided to go for the green, but sailed it right again. Gustafson finally reached the green, but lipped out a two-footer for par.
She shot a seven-under 64 and tied for fifth place with Morgan Pressel, who posted a five-under 66 on Sunday. The pair finished 54 holes at 12-under-par 201.
Lee made her move up the leaderboard with three birdies and a bogey over her opening-nine holes. She started her second nine with a birdie at the 10th, which took her to 11-under par -- one shot behind Gustafson.
Lee ran home a 25-foot birdie putt at the 11th to keep pace with Gustafson, who drained a 20-foot birdie putt of her own at the 14th. The Swede moved ahead again with a six-footer for birdie at No. 16, but Lee hung in with another 25-foot birdie putt at the 12th.
The 20-year-old rookie moved ahead for good when she rolled in a five-foot birdie putt at the 13th. Lee birdied four in a row after the turn and moved to minus-14.
Gustafson bogeyed the 18th to put Lee in command. Lee parred 14, 15 and 16, but especially scrambled at the par-three 15th. She was almost two clubs short with her tee shot, but she got up and down to remain at 14-under par.
At the par-three 17th, Lee hit her tee ball to four feet, where she sank the birdie putt. Barring a miracle, the tournament was Lee's, but she padded her margin of victory with a six-foot birdie putt at the last.
'I was a little nervous, but I kept concentrating on my game and then I didn't see a leaderboard,' said Lee. 'I didn't want the pressure.'
Becky Morgan (67) and Gloria Hee Jung Park (68) tied for seventh place at minus-nine. Mi Hyun Kim (68), Julieta Granada (68), Paula Creamer (68) and Patricia Meunier-Lebouc (70) shared ninth place at eight-under-par 205.
Second-round leader Ai Miyazato struggled in her quest for her first LPGA Tour victory. She carded a three-over-par 74 and was part of a group tied for 13th at minus-seven.