Na Yeon Choi fired an amazing 7-under 65 on Saturday in challenging conditions to build a huge lead after the third round of the U.S. Women's Open.

Choi finished 54 holes at Blackwolf Run at 8-under 208 and is six strokes clear of her closest competitor, Amy Yang, who posted a respectable, 3-under 69 Saturday.

Choi and Yang were the only players to break 70 Saturday at Blackwolf Run, but Choi's round was historic.

She matched the lowest third-round score in tournament history and her 65 tied the third-lowest round ever at a U.S. Women's Open.

"I had a really good feeling about my swing," said Choi, the fifth-ranked golfer in the world. "I had a really good round today. I think I hit a lot of good shots today. I wasn't nervous, and I focused on my game and I played it one shot at a time."

Lexi Thompson, the 17-year-old phenomenon, managed an even-par 72 and is tied for third place with Mika Miyazato (73) and Sandra Gal (74). The trio is knotted at 1-under 215.

Vicky Hurst shot a 3-over 75, which is good for sixth at even-par.

It was a terrible day for Suzann Pettersen, the 36-hole leader.

Pettersen made two double bogeys en route to a 6-over 78. She is tied for seventh with former champions Paula Creamer (71), Inbee Park (76) and Cristie Kerr (77). Lizette Salas (75) and Nicole Castrale (76) are also at 1-over 217.

"Feels bad to give away that many shots in that few holes," said Pettersen. "But it's a U.S. Open and hopefully -- well, I have a round tomorrow to make up for it. Today wasn't easy. Just made a few mistakes."

Michelle Wie, who started the third round in second place and was in the final pairing with Pettersen, also had a 78 on Saturday and fell into a tie for 13th at plus-2.

"Granted, it was playing really tough out there, but a little disappointed with my play today, but the thing is it's still the U.S. Open," said Wie, who has missed six cuts this year and hasn't cracked the top 30 in an event. "Na Yeon had a really awesome score today and we'll see what happens tomorrow."

World No. 1 Yani Tseng was not immune from the difficulties of Saturday. She had a 78 and is tied for 38th at plus-8, while world No. 2 Stacy Lewis shot an 80 and is 10-over for the tournament.

With these huge names in women's golf struggling, Choi was sensational.

She flew out of the gate on Saturday with a 3-foot birdie putt at one and a 15-foot birdie putt at No. 2. Choi rolled in a 20-footer for birdie at the par-5 seventh and found herself tied for the lead.

She didn't stay tied long.

At the par-3 eighth, Choi hit an 8-iron to 15 feet and drained the birdie effort to grab sole possession of first. She made a gutsy 7-foot par save at the ninth after doing what she could with a 70-foot birdie try, then kicked in a short birdie putt at the par-5 10th to go two clear of the field.

Choi continued her spectacular run with a pair of 5-foot birdie putts at the 11th and 12th. That was five birdies in a six-hole span around the turn and it also meant a four-shot lead.

Even Choi, as good as she was on this Saturday, couldn't keep a bogey off her card. She three-putted the 13th green from 50 feet, but with everyone tumbling down the leaderboard, she was still firmly in command.

Choi's last birdie of the round came at the par-3 17th. She hit a 7-iron to 15 feet and poured in the birdie effort. That gave her a six-shot lead and that's what it finished at when everyone got into the clubhouse.

"I had fun out there," said Choi. "I couldn't believe how I got eight birdies today, but I did. And I'm very happy, and I'm very satisfied and I'm very excited."

No one has come back from a six-shot deficit to win in the final round. Choi is a proven winner with five LPGA Tour titles, but none of those were majors and, even as comfortable as a six-shot lead is, there will be nerves on Sunday.

"I'm pretty sure I'll be nervous tomorrow," said Choi. "I have confidence and this is a good opportunity to be winning U.S. Open. I hope to get good warm up tomorrow morning and just go out there with my caddie and have fun."

Choi, like so many Korean girls, drew inspiration from Se Ri Pak, who triumphed here 14 years ago.

"I think after she won in June or July, even until like December, I watched it on the TV," said Choi. "I remember everything, that feeling, and I really want to continue that feeling."

NOTES: Defending champion So Yeon Ryo had a 2-over 74 and is part of group, along with LPGA Champion Shanshan Feng, at plus-3...Pak shot a 4-over 76 and is 5-over...Pace of play was an issue Saturday with the last pair taking almost six hours to complete the round.