Lewis, who won her first LPGA title of the year in Mobile, Alabama in April, had left herself with a seven-stroke cushion heading into the final round, after to back-to-back rounds of 65 on the first two days of the tournament.
Australia’s Katherine Hull sunk a 10-foot birdie on the final green secure second place, while Mika Miyazato and Azahara Munoz shared third after carding final rounds of 68 and 69 respectively.
"It was so hard out there," Lewis said. "Having a huge lead like that was really tough to keep your concentration, and I kind of lost it in the middle of the round." Lewis threatened to run away with the title when she birdied the third, fourth, seventh and eighth holes to extend her already mammoth lead over the front nine.
But a bogey at the ninth, followed by a double-bogey at the par-3 11th, where she missed an eight-foot bogey putt, and another bogey at the 12th threatened to derail the American’s round.
However, the 27-year-old regained her composure at the 13th, finally sinking a par putt before a 35-foot birdie putt at the 14th put her back into control.
"I know people don't like this, but I kind of slammed my putter after my three-putt on 12, and honestly, it relieved me so much," Lewis said. "It got all the tension that was in my hands. I was so stressed out and it just got all my tension out, and from 13 on, I felt great. I kind of got my rhythm back and got my feel back."