The 2013 winner at Desert Ridge, Lewis was 2 under through six holes Thursday when play was suspended because of darkness. After opening with a bogey on No. 7, she birdied Nos. 8, 9, 10, 12, 13, 15 and 16 and finished with an 8-under 64.
"It was just solid," Lewis said. "The golf course is in such good shape, you get some putts around the hole, you can definitely make them. Just hit a few close. I hit a 4-iron into about 6 inches, so that always helps."
The start Thursday was delayed four hours because of rain and wet conditions.
South Korea's Hyo Joo Kim was a stroke back. She played her final 12 holes Friday.
Top-ranked Lydia Ko, Tiffany Joh, Sophia Popov, Kim Kaufman and Karine Icher shot 66. Icher played her final 11 holes Friday.
Alena Sharp of Hamilton, Ont., opened with a 68.
The 17-year-old Ko has six LPGA Tour titles and 10 worldwide victories in pro events, winning the Women's Australian Open and the Ladies European Tour's New Zealand Women's Open in consecutive weeks this year. She nearly won last year at Desert Ridge, squandering a three-stroke lead with 13 holes left and ending up tying for second — a stroke behind Karrie Webb.
"I wasn't surprised Lydia shot what she did," Lewis said. "Just kind of motivated me to get up there with her."
The second-ranked Lewis had a 50-minute break before starting the second round.
"If you've got to play a lot of holes and you're on a roll, that's where you want to be," Lewis said. "Things feel good. It will be a quick turnaround."
Webb, also the 2011 winner, had a 67 playing alongside Lewis.
"Very solid," Webb said. "I feel like 5 under is perhaps the worst I could have shot, so that's always a nice thing to say. I felt very comfortable out there."
Michelle Wie opened with a 73 on Thursday. She's playing in a group with Ko.