Mo Martin earned a three-stroke lead as fellow American Michelle Wie missed the cut after the second round at the Women's British Open on Friday.
The diminutive Martin used her accuracy to avoid the punishing rough on her way to a second successive three-under-par 69 at Royal Birkdale in Southport, Lancashire.
But it was a different story for Wie, who carded 78 for a nine-over 153 total, three strokes too many to survive for the weekend.
"It was one of those weeks where I started off on the wrong foot, but stuff happens like that," Wie told Golf Channel.
"Golf is hard. I still feel good about my game. This doesn’t change how I look at my game but it’s also a good kick in the butt about what I need to improve."
Former child prodigy Wie, who just last month broke through for her first major title when she won the U.S. Women's Open, said her driving had let her down, despite a conservative strategy.
"My tempo got off this week. I just need to find it again. Nothing was too off this week. It’s just nothing was quite right. I just didn't hit the shots I needed."
Martin has gained a reputation as one of the straightest hitters in the women's game, and she played to her strength to post a six-under 138 halfway total.
The woman known as "Mighty Mo" has little experience of links golf, but she plotted her way to five birdies to break clear of Spaniard Beatriz Recari (67) and South Korean Ryu So-Yeon (70), who shared second place on three-under.
Women's world number one and defending champion Stacy Lewis was seven back.
(Reporting By Andrew Both in Cary, North Carolina; editing by Toby Davis)