Ariya Jutanugarn was alone in second place at 134 after firing a second consecutive 67. Suzann Pettersen was in third at 135 after a sizzling 65.
Tied for fourth at 136 were Ariya's older sister, Moriya Jutanugarn, two-time tournament champion Inbee Park and Marina Alex.
First-round leader Mi Jung Hur of South Korea followed an opening 65 with a 1-over 72 to fall into a tie for seventh at 137.
Lexi Thompson is playing for the first time since she lost the first major championship of the year three weeks ago on a rules violation called in by a television viewer.
Thompson is not off to a great start in the tournament, posting a 72 that included three birdies on the first five holes Friday for a two-day total of 142, which is nine strokes behind Nomura.
Nomura has two career wins in seven seasons on the LPGA Tour. Her best finish this year is a third-place tie at the Women's Australian Open.
The Japanese player logged six birdies on the back nine before her closing bogey. She also ended the front nine with a bogey.
"My mind was very calm today," Nomura said. "It was windy, but I like windy and tough conditions."
Ariya Jutanugarn is bidding for her first victory in 2017 after winning five times in 2016 as the tour's player of the year. The only blemish on her scorecard in the second round was a bogey at No. 8 to go with five birdies.
"Pretty good day today," Ariya said. "I hit the ball pretty good on my front nine, made some putts today."
Her older sister, Moriya, has never won on the LPGA Tour, with a best finish of fourth in the 2013 Women's Australian Open. Her round included a hole-in-one on the par-3, 135-yard No. 13.
Pettersen rebounded from an opening bogey on the second day with seven birdies.
Dori Carter set a tournament record with an 8-under 63. Her round featured a hole-out for eagle on the par-5 No. 3.
"I struck the ball well yesterday and I didn't get up and down," Carter said. "Today I did."
Defending champion Jenny Shin was 10 strokes behind after a 72.
With the threat of rain on Saturday, third-round play will be moved up, and the players will be grouped in threesomes.
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