Lewis, winner of the Ricoh British Women's Open at St Andrews earlier this year, fired eight birdies and just one bogey to finish nine under par at Emirates Golf Club, one shot ahead of Sweden's Pernilla Lindberg.
Lindberg, who shared the lead after the first round, added a 69 to her opening 67 to lie alone in second, a shot ahead of Spain's Carlota Ciganda.
Thailand's Pornanong Phatlum is another stroke back on six under before a three-shot gap to the chasing pack containing Scotland's Vikki Laing and English veteran Laura Davies.
Teenager Charley Hull, who is looking to secure Ladies European Tour rookie of the year honours in Dubai, carded a second round of 72 to lie seven off the lead on two under par.
Lewis said: "The putts went in today. I made a little adjustment on the practice green and it seemed to work. I made a couple of long ones that I probably shouldn't have made and it turned out to be a good day.
"On the longer putts the grip handle was stopping instead of keeping going so I changed that. I think I had 10 or 12 fewer putts and that made the difference. I'm going to have to keep going and take care of business but I prefer being where I am now to where I was last night."
Round two was suspended at approximately 5.45pm local time due to bad light and six players will return to complete their second rounds at 8am on Friday.