Lewis, No. 3 in the women's world golf rankings, had an eagle, eight birdies and a bogey in her opening round. Karine Icher, who had a bogey-free 66, is in second place.
Lewis opened with a pair of pars before dropping in her second shot for an eagle at the par-4 third hole. She ran off three consecutive birdies over Nos. 5-7 and closed the side with another birdie. She played the front nine par 4s in 5-under Thursday.
Lewis had birdies at 10 and 12 before slipping with a bogey at the 16th hole. However, she finished the round with birdies at 17 and 18 to build on her lead.
Icher had back-to-back birdies at Nos. 4 and 5 and again at 8 and 9. She added birdies at 13 and 18 in finishing the day alone in second.