The American followed up her opening 63 with a three-under par 69 to move to -12 for the tournament.
World number three Lewis produced a solid round with five birdies and two bogies.
She said: “It’s always hard to follow up a really good day.”
“I thought if I could shoot 4 or 5 under that would still be a really solid day. I almost got there but it was kind of up and down. I definitely left a few out there. I didn’t hit it as good today but I made some putts on the back nine and still have a three-shot lead so I can’t complain.”
Lewis leads by three shots over Thailand's Ariya Jutanugarn.
The 17-year-old wowed the home crowds with her precocious talent, producing a bogey-free round of 66 to move to nine under.