The 34-year-old American birdied four of her last six holes in the bogey-free round at Wilshire Country Club.
"I hit it good and putted well," Lewis said. "That's kind of the combination that's been missing, is just putting both of them together. Finally did it on the same day."
The 12-time tour winner missed the cut last year in the inaugural event, shooting 75-73.
Lewis didn't like the course setup last year but says organizers have made some improvements.
"Last year it was super firm and so I did not like the golf course," Lewis said. "Now the greens are much more receptive and you can just hit a lot better golf shots."
Green also had a bogey-free round.
"My ball-striking was great, but also my putter was really hot," Green said. "I was really happy with how I rolled it."
Her Australian compatriot Lee Min-jee Lee also went bogey free and was a stroke back.
"It was pretty solid all round," said Lee. "I just hit the greens and then if I was close, I would try and take opportunity of my birdie chances. If not, then I would be able to have a par."
Canada's Anne-Catherine Tanguay was just two strokes back of the leaders after shooting a four-under 67.
Tanguay's fellow Brooke Henderson, who won the Lotte Championship last week in Hawaii, was at 68 with Park In-bee, Feng Shanshan, Lizette Salas, Angel Yin, Isi Gabsa, Sarah Jane Smith, Jing Yan and Jasmine Suwannapura.