A late ruling took Inbee Park from one shot behind to leading the women's British Open on Saturday (local time), the slightest head start in her quest to become only the seventh player to win four of the LPGA Tour's major championships.
Park handled the tough opening stretch at Royal Birkdale with three birdies and shot a four-under 68, giving her a one-shot lead over fellow major champions Suzann Pettersen of Norway (68) and Shanshan Feng of China (69), along with Ahn Sun-Ju of South Korea.
Ahn appeared to be the player to chase after what she thought was a 69 for a one-shot lead.
She was summoned to the rules trailer, where officials determined she used her left foot to build her stance in a pot bunker left of the 18th green. Ahn was assessed two shots for violating Rule 13-3. Her par turned into a double bogey. Her 69 became a 71. And she went from a one-shot lead in the final group to having to make up ground against Park, the LPGA Tour's reigning player of the year.
The penalty also created a wide-open final round at Royal Birkdale.
Park was at four-under 212, though a dozen players were within three shots of the lead.
One of them was Charley Hull, the go-for-broke English teenager who made nine birdies early on Saturday for a tournament-best 66 that suddenly put her into contention to become the youngest major champion in LPGA Tour history. She was at one-under 215.
Also in the mix was Mo Martin, the 31-year-old American done in by a four-hole stretch on the back nine that sent her to a 77. She also was at 215, along with former US Women's Open champion So Yeon Ryu, who made one bad decision and one bad swing, both leading to double bogey.
Defending champion Stacy Lewis had a 70 and was three shots behind.
Park has been virtually ignored all week, a huge change from a year ago.
The 26-year-old South Korean had a chance at St Andrews last summer to become the first player, male or female, to win four straight majors in one season. The pressure and attention was enormous, and she wound up in the middle of the pack.
"I didn't have much pressure," she said of her week at Royal Birkdale. "Really just try to play my own golf. Yeah, I start to feel a little bit of pressure from now and tomorrow. But I'd rather be having the pressure than not being in contention."
Ahn took the outright lead with a 25-foot birdie putt on the 16th hole, and was poised to stretch the margin. Her approach into the par-five 17th was a yard too far to the right and barely tumbled into a bunker, forcing her to stand on the edge and stoop over to player shot from the sand. She made par.
And her penalty on the 18th began with a photographer who took a sequence of pictures at the top of her swing on her second shot. She caught it heavy and pulled it left, into the bunker, as she and her caddie looked back to see who was the culprit.
She blasted out of the sand and over the green, and did well to get down in two putts. Only later did officials determine she had built her stance.
"It's disappointing, but it's my mistake and I have to follow the rules of the game," Ahn said through an interpreter. "I still have a day to go and I have to stay focused and try my best tomorrow."
She said the ball was on the slope of the bunker and it was hard to make a stance.
"So what I was trying to do was fix a stance," she said. "But after the review, it was determined that I used my feet to try to make an even lie. My intent wasn't to break the rules. It was just to set my feet firm in the sand just to be able to make the shot. But that's the rule. There was no intent and I can't do anything about it."
A one-shot lead is next to nothing in golf. Three shots can disappear quickly. And what could make this Women's British Open go down to the wire is the finish at Royal Birkdale - three par 5s over the last four holes.
"You can make a double so quick on this golf course that you've just got to keep hanging in there," Lewis said. "I you get in trouble, get out, and just stay patient. If you make a bogey, it's OK, because you've got some par-five finishing holes here."
Martin opened with two bogeys, got them back with a pair of birdies, and then imploded with a double bogey at No 12, followed by three straight bogeys. Ryu also squandered a good chance. She tried to hit a hybrid out of the rough on No 13 and pulled it into a burn. From 118 yards out in the 16th fairway, she hit a poor wedge right of the green, knocked that 35 feet away and three-putted for another double bogey.
All of them are still very much in the hunt.
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