With the tough conditions, Choi was one of only five players to break par Friday.
HALF MOON BAY, Calif. (AP) -- Angela Stanford's rare double eagle turned into a huge boost for her to stay near the top of the leaderboard on a day when playing conditions were challenging for everybody.
A pair of double bogeys and a bogey on the 18th cost two-time defending champion Lorena Ochoa, who had a tough back nine after she began the day so well in the second round of the Samsung World Championship.
Na Yeon Choi of South Korea survived the changing wind and decreasing temperatures along the Pacific Ocean to shoot a 1-under 71 on Friday, giving her a 4-under 140 total and a two-stroke lead over Stanford (73), Ochoa (73), Paula Creamer (74) and Song-Hee Kim (73).
"It was really windy today and the weather got worse as we got later into the round," Choi said through a translator. "After two bogeys, I thought the game was getting away from me, but I looked at the scoreboard at the other players' scores and it gave me a calm confidence."
It took Ochoa all of three holes to find her touch Friday, then a few tough ones to lose the lead. Even her typically reliable long game deserted her on the back nine.
Ochoa birdied five straight holes from Nos. 4-8 to reach 5 under, and Creamer got to 6 under before things became especially difficult. At that point, they both thought they might be able to distance themselves a bit from the pack.
"You all saw the scores -- they just kind of dropped," Creamer said. "It played hard. It was a definite test of golf. You hit and hope. It was kind of like the British Open out there today."
Stanford, who also briefly got to 6 under, pulled off her double eagle on the par-5, 481-yard fourth hole -- only the second one this year on the LPGA Tour and the 30th in tour history. She hit a 7-wood from 212 yards. Katherine Hull, who also is in this elite 20-player field, had the other in the fourth round of the Michelob Ultra Open in May. There were only two total in 2007.
"I hit it exactly as I wanted to," said Stanford, whose painful left shoulder still bothers her on most shots. "I saw it bounce twice and heard it hit the flag and it disappeared. I said, 'Did that go in?' and they were yelling. I've never had a double eagle. It was much needed. It was a lot of fun."
Early on, it seemed like an ideal day for golf on the 6,450-yard Ocean Course at Half Moon Bay Golf Links, until the wind got strong. On Thursday, opening rounds were delayed for 26 minutes by dense fog. Rain was in forecast for Northern California overnight.
Both Ochoa and Stanford are coming off titles in Alabama -- Ochoa last week at Prattville and Stanford the previous week in Mobile for her second career LPGA title. She withdrew from last week's event because of the nagging shoulder injury that has affected her for about two years. She wasn't even sure she'd play be healthy enough to play this tournament.
Ochoa, among several players two strokes back to start the day, shot a 32 over the front nine but had several tough holes down the stretch, most notably the double-bogeys on 9 and 13.
"Of course I'm frustrated," Ochoa said. "I'm very upset I made those two double-bogeys. The conditions were the same for everybody. But it's only Friday and I'm close to the lead. I have to make sure I play well on the weekend. ... I didn't feel comfortable hitting my driver, and when you miss fairways here, you're done. I have to be more simple with my driver."
Five-time champion Annika Sorenstam, paired with Ochoa for the second straight day during the Swedish Hall of Famer's final Samsung, struggled mightily herself. She shot a 77 to drop to 2-over 146. Making things worse, she got stung by a wasp between the pinkie and ring finger on her right hand while on the second tee.
"When you start off a bad day like that, it seems like a big wasp," Sorenstam said. "It was hurting all day. It was just so typical, one thing after another. I was on the tee and it landed on my finger. I hit it and thought I killed it, but he got back at me. ... I want to perform and I haven't. That's more mentally draining on me."
Ochoa tried for the green off her approach on the 500-yard, par-5 eighth hole -- the fourth-longest on the course -- only to have it roll back down a hill, but she then chipped to within 10 feet and sunk the birdie putt to move to 8-under.
The large gallery following the twosome featured many fans from her native Mexico and they chanted phrases such as "Si se puede!" -- We can do it! -- and "Vamos!" -- let's go! Ochoa shook her head to acknowledge the supporters.
But on No. 9, a par 3, Ochoa's drive sailed right just off a bunker and she chipped out of it and past the pin into the thick, sticky rough. She had another tough go on 13.
Creamer, meanwhile, had four bogeys on the back nine including three straight from 15-17 before finishing strong with a birdie on 18.
South Korea's Ji-Yai Shin, who won the Women's British Open in August, fell back with a 76 after leading through the first round. She was 1 under along with Hull (73) and Yani Tseng (74).