Scotland's Mhairi McKay turned in a surprising performance on Thursday with five straight birdies and a 5-under 66, giving her a three-stroke lead to match the largest 18-hole margin in the US Women's Open.
In an Open dominated by talk about teenagers, 17-year-old Aree Song, of Thailand played with experience beyond her years for a 1-under 70.
She was tied with 15-year-old Morgan Pressel, who played bogey-free golf on a wicked Witch Hollow course at Pumpkin Ridge until a double bogey on the final hole dropped her to 1-under 70.
The 18-year-old Irene Cho is another stroke behind.
Michelle Wie, at 13 perhaps the most heralded of the teenagers, blasted drives over 300 yards and finished with a birdie on the tough ninth hole for a 73.
The big Hawaiian played in the final group of the first LPGA major, the Nabisco Championship, and the others look like they want a piece of the action.
"Great, great talent," McKay said of the 14 teenagers at Pumpkin Ridge, which the USGA believes to be a record. "They're probably looking at Michelle and gaining confidence."
Now, they could look all around Pumpkin Ridge.
Of the 14 teens, 10 shot no worse than 76 -- the average score on an otherwise punishing afternoon at Pumpkin Ridge.
Defending champion Juli Inkster, a 43-year-old with a daughter the same age as Wie and Sydney Burlison (81), birdied the final hole for a 69.
She was tied with Donna Andrews, while Annika Sorenstam of Sweden had to scramble for a 72.
Inkster said experience only helps if shots are finding the fairways and greens.
"I could have the most experience in the world, but if I'm not hitting the shots, it's not going to pay off," she said. "It's a four-day tournament. You've just got to stay in the ballgame. That's what they're doing."
McKay has been working hard on her swing, and it came together at an opportune time. She made four straight birdies with wedges in her hand, then finished off her string with a 5-iron into 4.5m at No. 16.
The three-stroke lead was the largest after the first round of the US Women's Open since Helen Alfredsson in 1994.
McKay stumbled down the stretch, hitting a poor drive on the 16th that led to bogey, and missing the green on the 17th for another bogey.
But she ended in style on the 452m 18th, clearing the hazard with her second shot and leaving herself a delicate pitch from the left rough. The ball came out high and soft, landed on the front of the green and grazed the left lip before stopping 1m away.
After tapping in for her eighth birdie of the round, McKay turned to the crowd on both sides, then tossed her ball into the grandstand.
It was only the second time she had shot in the 60s at a Women's Open, but McKay knows better than to get overly excited.
"It's Thursday," she said, holding out her arms to quell the optimism. "You can't get too far ahead of yourself."
No one can ever be too far ahead of Sorenstam, who scrambled out of a tough start with three straight birdies. The best player in women's golf closed on a disappointing note, three-putting from 12m for bogey to finish 1 over par.
That left her six shots out of the lead, and behind three teenagers.
"I'm tired," Sorenstam said. "I was thinking on every shot."
Song was known as Aree Wongluekiet -- her mother's Thai surname -- when she played in the final group of an LPGA major at the 2000 Nabisco Championship as a 13-year-old, winding up in a tie for 10th.