The American’s brilliant round, which included seven consecutive birdies and nine overall, put her ahead of South Korea’s Hee Young Park, tying the course record in style.
''I didn't really have anything going the first few holes. I don't know what changed or clicked,'' Lewis said.
''It was just one of those days where you get into this rhythm. I was more happy to finish with the two birdies than even the seven, just to get some momentum going into tomorrow.''
Lewis, who has won twice on the LPGA Tour this year, is the second woman to hit a 63 on the course after Helen Alfredsson in 2008.
The 27-year-old’s previous lowest round was 64, which she made in the second and final rounds while winning the ShopRite LPGA Classic in June.