China's Feng Shanshan shook off persistent rain and the commotion of a presidential visit on Friday to fire a two-under par 70 and stretch her US Women's Open lead to two strokes.
Feng had three birdies and a bogey for an eight-under par 36-hole total of 136.
That was good enough for a two-stroke lead over South Korea's Lee Jeong-Eun6, Amy Yang and Choi Hye-Jin, who all shared second on 138.
Choi, a 17-year-old amateur, teed off on 10 and joined Feng atop the leaderboard after a burst of four straight birdies at 18, one, two and three. But she faded with bogeys at the seventh and eighth to join her compatriots on six-under.
Lee, last year's KLPGA Rookie of the Year playing her first tournament in the United States, set an early target with a second straight 69 on a rainy morning at Trump National Golf Club.
She birdied the second, took her lone bogey at the fifth but closed the front nine with a birdie and added back-to-back birdies at the 14th and 15th.
She was eventually joined by Choi and Yang, who went into the second round one stroke behind Feng and fired a second-round 71.
Feng said she wasn't bothered by the sometimes heavy rain that fell through much of her round, and she didn't get too distracted to the arrival of US President Donald Trump, who has made his namesake club in Bedminster a frequent weekend retreat this summer.
Trump arrived in a motorcade fresh from a Bastille Day trip to Paris, and watched from an enclosed viewing area near the 15th green, offering a few waves for cheering fans who eagerly snapped his picture.
"I heard people like kind of screaming, so that's what I was trying to find out, like why they were screaming," Feng said of the movement around the green, where marshals had to remind the gallery that play was continuing.
"But I was still really focusing on my game," Feng said. "I didn't really get distracted."
Trump's visit marked the first time a sitting president has attended the US Women's Open, and the US Golf Association was unrepentantly welcoming despite the controversy sparked by Trump's controversial remarks about women during his presidential campaign.
While there were fears his visit would spark protests, fans at the course were supportive and players apparently unfazed.
The morning rain -- on the heels of Thursday thunderstorms that disrupted play and caused the first round to be carried over until Friday morning -- was more of a challenge.
- Well-prepared -
Feng coped admirably, playing her first 10 holes in even par, with one birdie and one bogey, before back-to-back birdies at the 11th and 12th.
"I played probably the first nine holes in the rain, but my phone told me it was going to rain all afternoon and I was prepared," she said. "I really didn't pay attention to the weather and just concentrated on every shot."
The rain-soaked course did play longer, Feng said, which she admitted "made me feel like I was older".
Among Feng's closest pursuers, Yang is seeking a first major title after 16 top-10 finishes.
Lee -- the '6' in her name distinguishing her from five other KLPGA players with the same name -- is hoping to make a splash in her first US tournament.
Choi, the second-ranked amateur in the world, is also hoping to stay in the hunt at the weekend for what would be a sensational major win.
The trio sharing second were followed by another South Korean, with Bae Seon-Woo alone in fifth after a 69 for 139.
World number one Ryu So-Yeon carded an even par 72 to join four players sharing sixth on 140 that also included South Korean Chun In-Gee, Japan's Haru Nomura and Spain's Carlota Ciganda.