So maybe this experience thing is a tad overrated.

The long-held expectation is that players needed to endure an apprenticeship before contending for U.S. Women’s Open titles.

But that doesn’t seem to be the case lately, especially among players from  the Republic of Korea.

In Gee Chun claimed last year’s championship at Lancaster (Pa.) Country Club, carding a final-round 66 to edge countrywoman Amy Yang by a stroke. And Birdie Kim holed out a bunker shot on the 72nd hole to win in 2005 at Cherry Hills Country Club. Both were rookie competitors.

This year, Sung Hyun Park has put herself into position to become the fifth golfer – and the second in as many years – to win the Women’s Open in her first start. Following a 6-under-par 66 on Friday at CordeValle, the 25-year-old grabbed the midway lead by two strokes over countrywomen Yang and first-round leader Mirim Lee. Park stands at 8-under 136 and is one of seven players in the field to shoot under par both days.

There are, however, several other challengers closely on Park’s heels who will try to apply major-championship pressure. The biggest threat could be world No. 1 Lydia Ko, 19, of New Zealand, who rebounded from a disappointing first-round 73 to match Park’s 66 and move from a tie for 52nd to a share of fourth, just three strokes behind Park. It was Ko’s lowest score in 18 Women’s Open rounds, bettering the 68 she posted in the final round last year.

Then there’s Yang, a two-time U.S. Women’s Open runner-up (2012 and 2015) who has top-10 finishes in five of her last six starts. Despite a bogey on her final hole, Yang carded a 71.

Lee, 25, couldn’t match her brilliant 64 from Thursday, but a 2-over 74 in Round 2 has the two-time LPGA Tour winner in a tie for second.

Among the top nine on the leader board, only Ko and 2009 Women’s Open champion Eun-Hee Ji, of Korea, own a major championship. Ji, who shot a 71, is tied for sixth at 4-under 140 with Americans Jessica Korda (70) and Danielle Kang (69), and Kelly Tan (72), of Malaysia.

The cut came at 4-over 148 with 72 players (69 professionals and three amateurs) earning a chance to play the weekend. Chun, bidding to become the first repeat champion in 15 years, bogeyed her final two holes to shoot 77 and miss the cut by two.

Just like on Thursday, the morning wave took advantage of benign winds and slightly softer conditions, and the scores reflected it. Nineteen sub-par rounds were recorded compared to only three in the afternoon. The low score of the afternoon, a 3-under 69, belonged to Haru Nomura, 23, of Japan, a two-time winner on the LPGA Tour in 2016 who is tied for fourth with Ko. On Thursday, 23 of the 37 sub-par rounds were from the morning wave.

“I think today course was tough, like too much wind,” said Lee, who played in the afternoon. “And so I keep trying to hit the fairway and the green, but I couldn't. So the score, it's not bad, but not good, either.”

Park might be a relative newcomer to the U.S. stage – she only has three starts on the LPGA Tour in 2016 – but her game has already made headlines in Korea. She posted three victories on the LPGA Tour of Korea last year, including the Korean Women’s Open. Park added two more KLPGA victories this year: the Hyundai China Ladies Open and Samchully Together Open.

Even in her limited LPGA Tour starts, she has been impressive, finishing no worse than a tie for 13th (JTBC Founders in Arizona). She also tied for sixth in her only major-championship start of 2016, the ANA Inspiration in Rancho Mirage, Calif.

Those finishes have vaulted Park to No. 18 in the Rolex Women’s World Golf Rankings, one of 10 Koreans who occupy the first 20 positions.

Park played bogey-free golf for 16 holes on Friday until a bogey on 17. On the par-5 18th, she drove the ball into a hazard, yet managed to salvage par by holing a 12-footer.

“Coming to the tournament, I didn't even think about winning because this is the first time for me,” said Park. “I would like more experience with the USGA, LPGA. But I'm trying to enjoy this tournament. That's why I am just more comfortable. I just enjoy the play. That's why it happened today.”

Ko, looking for a third major after winning the Evian Championship last fall and the ANA Inspiration in April, seemingly enjoys herself every time she tees it up. But her mood got even brighter with a seven-stroke turnaround from Thursday. Among those in the early wave, Ko overcame an early bogey on the par-4 first by rattling off four consecutive birdies from No. 3. Her wedge approach on the par 5 stopped inches from the flagstick, and she proceeded to shoot a 4-under 32 on the outward nine.

The birdies weren’t as plentiful on the second nine, but she finished the day off in style, stuffing a wedge approach to 4 feet for a birdie.

“My birdie on 3 kind of turned the round around and making the string of birdies definitely helped,” said Ko. “Just to know that this is the first time I was under par for the tournament put me in a positive position. I just tried to enjoy it out there. I think the whole group played a little better than yesterday. So that kind of gave a little bit more of a momentum.”

Playing alongside world No. 2 Brooke Henderson, 18, of Canada, and world No. 4 Lexi Thompson, 21, of Delray Beach, Fla., the three young stars performed better in Round 2. Henderson shot 71 and Thompson 73, improving by four and one stroke, respectively, to make the cut.

“We were talking around, joking around,” said Ko of the grouping with a combined four major titles. “We've played together a few times throughout the year, so we're used to each other. So it was good. And I think we all enjoyed it.”

More happiness could be on the docket in the next 48 hours.

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