Pornanong Phatlum carded a 6-under 66 on Friday and remained one stroke clear of the field after two rounds of the Safeway Classic.
Phatlum is going for her first official LPGA Tour victory. She did win the unofficial event in Brazil last year.
Suzann Pettersen fired a 9-under 63 in round two to jump into second place at minus-13. Sandra Gal posted her second straight 66 and is alone in third at 12-under-par 132 at Columbia Edgewater Country Club.
Caroline Masson is alone in fourth at minus-11 after firing a 64 in round two.
Sandra Changkija (66), 2008 champion Cristie Kerr (68) and Lizette Salas (68) share fifth at 10-under-par 134.
Phatlum had a steady start with four pars in a row from the first. She birdied the fifth and seventh, both par-5s, to move to 10-under par.
Around the turn, Phatlum birdied the par-5 10th. At the last par-5, the 12th, she finally made her first par. That was one of four straight pars from the 11th.
Phatlum converted back-to-back birdies at 15 and 16. She drained a birdie effort at the last to post 14-under.
"I played kind of good today, but my putter wasn't that hot. I didn't hit it close enough to the pin, so I didn't make enough birdies on the front nine," Phatlum admitted. "But then I started getting on a roll and then I made more birdies on the back."
Pettersen put together a bogey-free round that started with three birdies in her first four holes from the 10th. She later birdied the 16th and 18th to head to the front nine at minus-9.
The 2011 Safeway Classic winner picked up birdies at the third and fifth to move to minus-11. Pettersen closed with birdies at seven and nine to end one back.
"Today was a great round on the greens. I kind of fed off Beatriz's start," said Pettersen, who played with her Solheim Cup teammate Beatriz Recari, who birdied five in a row to start her round.
"She had five pretty quick birdies. It was kind of nice to get everyone going early. Compared to yesterday, I decided when I made the turn to just kind of keep giving myself looks, keep giving myself chances, and I pretty much made every good look that I had. One of my better putting performances here."
NOTES: Defending champion Mika Miyazato carded her second straight 71 and made the cut on the number ... Eighty-five players made the cut, which ended at 2- under-par 142 ... Among those that missed the cut were Karen Stupples, Laura Davies, Christina Kim and Sophie Gustafson, who announced her retirement afterwards.