SAN FRANCISCO, April 26, 2014 (AFP) - American Lewis finished 36 holes at Lake Merced Golf Club at six-under-par 138.
"We knew it was going to be a long day," said Lewis who earned three victories in 2013. "That's the way I took it, one shot at a time and tried to get the ball in the hole.
Second round play was stopped for 80 minutes because of a rain storm.
"That's what I tried to do. Get it in the hole as fast as I could. Fortunately I was able to do that and make a couple putts."
First-round leader Karine Icher of France shot a one-over 73 and is tied with Kiwi Lydia Ko (71) for second place at five-under 139.
World number one Park In-Bee of South Korea tied the low round of the day with a four-under 68 to jump into a share of fourth with Lee Il-Hee (73) and Mika Miyazato (69) at three-under 141. Suzann Pettersen (72) is among nine players tied for seventh at two-under.
Pettersen was joined by P.K. Kongkraphan (68), Catriona Matthew (69), Kang Hae-Ji (70), Brittany Lang (71), Paola Moreno (71), Carlota Ciganda (72), Kim Hyo-Joo (73) and Jenny Shin (74).
Lewis, who began on the 10th hole, opened her round with six straight pars before rolling in back-to-back birdies at the 16th and 17th to move to five-under.
She birdied the eighth to reach six-under and parred the last hole.
Icher followed five straight opening pars with a bogey at the sixth to fall to five-under.
She parred her final four holes to finish at five-under.
"It's a tough golf course," Icher said. "You can be quick in trouble, or if you're playing well, like yesterday I did think it goes pretty well -- but today with the wind and the rain it's definitely a tough day."
Leading second-round scores on Friday from the LPGA Tour's Swinging Skirts Classic. (USA unless noted, par-72):
138 - Stacy Lewis 69-69
139 - Karine Icher (FRA) 66-73, Lydia Ko (NZL) 68-71
141 - Inbee Park (KOR) 73-68, Mika Miyazato (JPN) 72-69, Ilhee Lee (KOR) 68-73
142 - Catriona Matthew (SCO) 73-69, Suzann Pettersen (NOR) 70-72, Brittany Lang 71-71, Carlota Ciganda (ESP) 70-72, Paola Moreno (COL) 71-71, P.K. Kongkraphan (THA) 74-68, Jenny Shin (KOR) 68-74, Haeji Kang (KOR) 72-70, Hyo-Joo Kim (KOR) 69-73
143 - Hee Young Park (KOR) 70-73, I.K. Kim (KOR) 72-71, Ashleigh Simon (RSA) 73-70, Mo Martin 69-74, Alison Walshe 74-69, Christel Boeljon (NED) 69-74, Line Vedel (DEN) 72-71