Stacy Lewis turned in a second-round 69 on Friday to maintain a 3-stroke lead at the Honda LPGA Thailand
The world No. 3 Lewis is now 12-under 132 through 36 holes.
"I definitely left a few out there," said Lewis. "I didn't hit it as good today, but I made some putts on the back nine and still have a 3-shot lead so I can't complain."
Ariya Jutanugarn, who is playing courtesy of a sponsor invite, vaulted up the leaderboard with a second-round 66 at Siam Country Club's Pattaya Old Course. The Thailand native began Friday in a tie for 10th place and ended alone in second at 9-under.
So Yeon Ryu, ranked eighth in the world, and Beatriz Recari both shot 68s to end 36 holes at 8-under. They are tied for third place with Catriona Matthew, who carded a 69.
Lizette Salas birdied three of her first four holes on Friday and later added an eagle on the par-5 10th to get within a stroke of Lewis, but she faltered with a pair of bogeys down the stretch and finished with a second-round 69.
Se Ri Pak (68) is tied with Salas at 7-under, while world No. 4 Inbee Park (71) is a stroke back in eighth place. Park was tied for third entering Friday after an opening-round 67.
Fifteen-year-old amateur sensation Lydia Ko and last year's runner up Ai Miyazato both carded 71s to move into a tie for ninth place at minus-4. Ko recently won the New Zealand Women's Open to become the youngest victor in Ladies European Tour history, while Miyazato was a 2010 champion at this event.
Karrie Webb (71) and Jessica Korda (67) also sit at 4-under.
World No. 1 and two-time defending champion Yani Tseng rebounded from her opening-round 75 with a 68 on Friday. Last year, Tseng carded a 73 in round one, but rallied with back-to-back 65s in the second and third rounds to jump back into contention.
Joining Tseng at 1-under is Jiyai Shin, who bested the former at last week's season-opening Handa Women's Australian Open and jumped to No. 6 in the world as a result. Shin has turned in rounds of 70 and 73 thus far.
Lewis, who finished tied for 15th last week in Australia, immediately added to her lead on Friday with a birdie on the opening hole. The 2012 LPGA Tour Player of the Year then cooled with four straight pars, allowing Salas to get within three stokes courtesy of her scintillating start.
A birdie on the sixth got Lewis to 11-under, but she closed her outward nine with a bogey as Salas was executing her eagle on the 10th; a feat which quickly narrowed the margin to a single stroke.
Lewis, though, rebounded with back-to-back birdies at the start of her back nine. She then bogeyed the par-4 14th, but her birdie a hole later, coupled with Salas' dropped shots on Nos. 13 and 17, negated the threat.
"I think I've gotten a lot more comfortable having the three-shot lead. In the past you get up and you kind of start protecting a little bit and you realize you still have to go out there and hit shots," Lewis said. "You can't be complacent with it. You just have to go out there and play and not worry about what anyone else is doing. I didn't look at many leaderboards today until kind of the last few holes. I think I'll probably continue to do that."
NOTES: With her win at the New Zealand Women's Open, Ko became the youngest victor in Ladies European Tour history. She finished third last week in Australia ... Jutanugarn's sister Moriya, an LPGA rookie, is 2-over through 36 holes ... The field this week is comprised of 70 players -- 60 LPGA Tour players and 10 sponsor invites ... Michelle Wie finished second here in 2011. She is 1-over ... Last year, Tseng closed with a 6-under 66 to overtake Ai Miyazato. Tseng also won this title by five strokes in 2011.