Lydia Ko nearly had a disastrous situation late in Saturday’s third round of the 71st U.S. Women’s Open Championship. The world’s top-ranked female golfer fumbled her wedge near CordeValle’s 17th green and it nearly struck her ball. It led Fox Sports golf analyst Paul Azinger to comment that Ko’s heart rate must have gone up a few beats.

For the normal golfer, yes, but not Ko. In typical fashion, Ko laughed off what could have been a one-stroke penalty – had the club touched and moved the ball – by calmly getting up and down for par.

“She’s not the most coordinated, believe it or not,” said caddie Jason Hamilton. “[But] she’s got a good sense of humor. If things go amiss, she’s pretty good at laughing it off most of the time and getting on with the next shot.”

That cool demeanor, along with a world-class short game, has the 19-year-old from New Zealand in prime position to become the youngest champion in U.S. Women’s Open history. The 13-time LPGA Tour winner followed her second-round 66 on Friday with a 2-under 70 to grab a one-stroke lead over 2009 Women’s Open champion Eun Hee Ji and first-time competitor Sung Hyun Park, both from the Republic of Korea.

Ko, who has claimed two of the last three major championships and was the runner-up in the other (last month’s KPMG Women’s PGA), sits at 7-under 209.

American Brittany Lang, the runner-up in 2005 as a 19-year-old amateur, and two-time U.S. Women’s Open runner-up Amy Yang, of Korea, are two strokes behind Ko, while 2003 runner-up Angela Stanford, of Saginaw, Texas, is alone in sixth at 4-under 212.

Two-time U.S. Women’s Amateur champion Danielle Kang, a California native who resides in Las Vegas, Nev., is in solo seventh at 213.

A group of seven players that includes two-time major champion Stacy Lewis, 2007 Women’s Open champion Cristie Kerr and three-time LPGA Tour winner Ariya Jutanugarn, of Thailand, is another stroke back at 214.

All are chasing a player who somehow always appears unflappable. Ko admits to having nerves, but from the outside, it doesn’t appear as though she realizes she is competing in the biggest championship in women’s golf.

“I look a lot calmer than what goes on in the inside,” said Ko. “I definitely do get nervous, but I think that's part of it. Nerves are good, actually … because it means you're excited. You're ready. It means a lot to you. Obviously you've got to be able to control [nerves]. I just try and take deep breaths.”

Ko admitted to having uncontrolled anxiety four years ago when she competed in her first Women’s Open at Blackwolf Run and finished as the low amateur. So much has changed since then. That summer, she won the U.S. Women’s Amateur, then the CN Canadian Women’s Open to surpass Lexi Thompson as the youngest winner of an LPGA Tour event at 15 years, 4 months. Last fall at the Evian Championship, she surpassed Morgan Pressel to become the youngest major champion at 18 years, 142 days by shooting a final-round 63. It was one of five victories for Ko in 2015.

Another major followed in April at the ANA Inspiration, and only a brilliant final-round 65 by Brooke Henderson kept Ko from a third consecutive major title last month at the KPMG Women’s PGA Championship. Henderson prevailed in a playoff over Ko, who had held the 54-hole lead.

Ko entered Saturday’s third round three strokes behind 36-hole leader Park, and by late in the second nine, Ko had caught her, thanks to a 25-foot birdie at No. 13 and a 30-foot par save at the 14th hole. Like 2015 U.S. Open champion Jordan Spieth, Ko possesses a deft touch on the greens, which masks her relatively short length off the tee (she ranks 59th this week in driving distance and 117th for the season on Tour).

But she is No. 1 on the LPGA Tour in scoring average (69.08) and she hasn’t three-putted a green this week.

“I’ve seen a couple of other players who could roll the rock pretty good,” said Hamilton, an Australian who previously caddied for five-time major champion Yani Tseng before picking up Ko’s bag two years ago. “She’s just as good as all of them. Her stroke is just as good under pressure, which is key. Most people get a little tight and quick. She’s able to keep it relaxed.”

Park, 22, looked very much under control until the ninth hole, when she blocked her 3-wood tee shot on the par 5 into a hazard right of the fairway, leading to a double-bogey 7. She played 1-over golf into the clubhouse, with her lone birdie coming when she reached the par-5 15th in two and two-putted from 20 feet.

“I felt comfortable and I wasn't as nervous as I thought I would be,” said Park, who shot 74 after a 66 on Friday and is trying to become the fifth golfer to win the Women’s Open in her first appearance, and second in as many years (In Gee Chun). “I am disappointed by the putting, but the difficult environment was the wind going on today.”

Much like the first two days, conditions dried out as the wind and sunshine increased. Early starters like Lang, Lewis and Jutanugarn took advantage, shooting 68, 69 and 69, respectively. But Ji, who birdied the 72nd hole at Saucon Valley Country Club in Bethlehem, Pa., to edge Candie Kung by a stroke in 2009, quietly carded a third consecutive under-par score in the third-to-last grouping. The 30-year-old played her final nine holes in 2-under 34 to get into Sunday’s final grouping with Park and Ko.

“I just focus on my game,” said Ji, one of two players, along with Stanford, to have three sub-par rounds this week. “I’m trying to play my game and trying to be patient out there. Yeah, that's all.”

Ji knows what it’s like to be in contention at a major championship on Sunday. So does Ko, who slept on the 54-hole lead at the KPMG last month, and came from behind to win the Evian and the ANA Inspiration. Don’t expect her disposition or preparation to change.

“I'm going to get some physio just to loosen up the body,” said Ko of her evening plans. “And whatever Mama Ko is cooking up, it’s good to my taste buds to have that. Just before I leave [CordeValle] maybe hit a few balls or maybe a few putts, but not anything crazy. Maybe watch a [TV] program, just something relaxing.”

Don’t expect any late-night gallivanting. After joking in a post-round interview that she planned to “party all night and come straight to the course,” Ko recounted attending a midnight concert last December by Psy, the Korean singer best known for humorous videos and stage performances. Ko, who was joined by her older sister and Australian golfer Su Oh, came home at 5 a.m. with a sore throat.

“I took advantage of the off-season,” said Ko, smiling. “Christmas Day was the only day I did nothing and just chilled out. I’m too young for clubbing, anyways.”

But not too old to win majors and hoist trophies. On Sunday, she could add the biggest prize of her ever-growing collection.

David Shefter is a senior staff writer for the USGA. Email him at dshefter@usga.org.