Lewis birdied the 14th, 16th and eighth holes after starting on the back nine at Pinehurst in North Carolina, to sit a shot ahead of fellow American Michelle Wie when the first round of the US Open was halted.
Rain stopped play on Thursday with 30 players yet to finish their opening rounds and Lewis was thrilled to have claimed an early lead, as she aims for the third major title of her career.
"I just have geared my game towards majors," the 29-year-old said.
"I love it when it's hard. I love it when you have to grind. I love it when you have to make eight- and 10-footers for par. It suits me and my game."
Wie had a far more inconsistent round, claiming a birdie on the second hole before bogeying the fifth and seventh.
The 24-year-old from Hawaii hit back with birdies on the 10th, 12th and 14th holes, before dropping a shot on the 16th and reclaiming it on the final hole.
The birdie on the par-four 18th saw Wie finish with a 68, one shot ahead of Australian pair Katherine Kirk and amateur Minjee Lee, plus South Korea's So Yeon Ryu.
Another Australian - Karrie Webb - is a shot further back at even par, sharing sixth with Paula Creamer, while Candie Kung of Chinese Taipei, England's Stephanie Meadow and Mina Harigae of the United States are also in that group but have first-round holes to play.