Chun began the final round four shots back of Yang, the overnight leader, but poured in three birdies over her final four holes for the narrow victory.

Chun became the seventh South Korean champion of the U.S. national championship after Pak Se-ri (1998), Birdie Kim (2005), Park In-bee (2008 and 2013), Ji Eun-hee (2009), Ryu So-yeon (2011) and Choi Na-yeon (2012). Chun is a full-time member of the Korean LPGA Tour and is currently leading the domestic circuit in money.

She turned pro in 2012 and has seven wins on the Korean tour, including three in 2015. She also has a win on the Japanese LPGA Tour this year, becoming the first South Korean since Shin Ji-yai in 2008 to win on all three tours in the same year.

Chun is projected to jump from No. 20 to No. 10 in the women's world rankings.

In 2015 alone, six South Koreans have combined for 10 LPGA victories in 17 tournaments so far, with Chun being the third straight winner after Park In-bee at the KPMG Women's PGA Championship and Choi Na-yeon at the Walmart NW Arkansas Championship last month.

Chun had three birdies against one bogey on the front nine, and she looked to have shot herself out of contention with a bogey on the 10th.

A birdie on the par-3 12th gave Chun some hope, and she reeled off three consecutive birdies starting on the 15th.

Playing ahead of Yang, Chun finished her championship with a bogey but still got the victory when Yang also committed a bogey on the same hole.

Yang still held the lead until the 14th, where she had her fourth bogey of the day and dropped into a three-way tie at the top with Chun and Stacy Lewis at six-under. Yang bogied the next hole before rallying with an eagle on the par-4 16th and a birdie on the 17th.

Yang entered the 72nd hole tied with Chun but had a disastrous bogey there to finish alone in second place.

Chun said scoring a birdie on the 15th for the second consecutive day fueled her back-nine charge.

"I had a birdie opportunity on the 15th on all four days, and I was feeling great playing that hole today, too," she said. "On the final hole, I got into deep rough (off the tee). I wanted to play it safe and punch it out to the fairway, and hit a solid third shot. This was a long course (at 6,406 yards) with thick rough, and missing the fairway would make life difficult. Fortunately, I hit good shots all week and didn't miss much."

This was Chun's first U.S. Women's Open appearance. She is only the third player to win in her debut after Kim in 2005 and Kathy Cornelius in 1956.

As a non-member, Chun has made five starts on the LPGA Tour in 2015 and has made cuts in all five, with $842,075 in earnings.

Dating back to 2012, 10 of the past 17 LPGA majors have been won by South Korean golfers.

Two-time champ Park In-bee finished tied for third with Lewis at five-under, while another former champ, Ryu So-yeon, ended in a six-way tie for fifth at three-under. (Yonhap)