LANCASTER, Pa. » South Korea’s In Gee Chun birdied four of the last seven holes to rally for a one-stroke victory at the U.S. Women’s Open on Sunday.

The 20-year old Chun shot a 4-under 66 in the final round and finished at 8 under, becoming the first player to win her U.S. Open debut since Birdie Kim in 2005. It was her fifth victory this year.

Third-round leader Amy Yang struggled in the middle of her round and then pulled within one by going eagle-birdie at Nos. 16 and 17. But she bogeyed the 18th and fell a stroke short.

Playing in the final group on the last day of the championship for the third time in four years, Yang squandered a three-stroke lead and settled for a 1-over 71 and second at 273.

Two-time champion and top-ranked Inbee Park (67) overcame putting woes and rallied late, tying for third with Stacy Lewis (70) at 5-under 275.

Defending champion Michelle Wie battled hip and leg injuries and limped in with an even-par 70, placing 11th at 2-under 278.

With most of the focus on the final pairing of Yang and Lewis, Chun, playing a group ahead, quietly picked up strokes on the leaders. At 4 under heading into the final round at Lancaster Country Club, Chun picked up two strokes on the front nine, closing within two of the lead.

She got within a stroke with a birdie at the 12th, and then rolled in a nine-foot putt at No. 15 for the first of three straight birdies. She moved into the lead with a birdie at 16 as Yang and Lewis struggled. She added another birdie at the 17th to stretch her lead to two strokes.

At the troublesome 421-yard, uphill closing hole, Chun drove into the rough, chipped short and went on to make bogey, falling into a tie for the lead with Yang, who birdied 17.

But Yang failed again in her bid to claim the biggest prize in women’s golf. She also drove into the rough at the last hole, chipped short of the green and failed to get up-and-down for par, giving Chun the win.

Lewis’ bid for her first U.S. Open title was foiled by a pair of double-bogeys, with the most costly one coming at 15, a hole after she had moved into a tie for the lead. At the 15th, she drove into the rough, hit her second shot through the fairway, and then dumped her third shot into a greenside bunker before taking a 6 and falling out of contention.

Park had three birdies on the back nine. Within two shots of the lead through 16 holes, the putting woes that dogged the 2008 and 2013 winner returned and her bid ended with a three-putt bogey at the 17th.

Wie grimaced in pain throughout the round. The nagging left hip and leg issues that have made this a forgettable season for the 25-year-old four-time LPGA Tour winner seemed to intensify in the final round.

Wie repeatedly cringed and tried to take weight off her right side after drives. Her final round did have one highlight, with her drive at the 234-yard, par-4 16th hitting the flagstick before she rolled in the short eagle putt.

Megan Khang was the championship’s low amateur. The 17-year-old from Rockland, Massachusetts, closed with a 1-over 71 and finished at 5-over 285. She bested Mariel Galdiano, a 17-year-old from Hawaii, by a stroke.

Fan favorite Laura Davies, who is to be inducted into the World Golf Hall of Fame at St. Andrews on Monday, closed with her worst round of the championship, a 5-over 75. The 1987 champion, who was the oldest player in the field at 51, finished at 7-over 287.

Canadian teenager Brooke Henderson helped her bid to lock up LPGA Tour playing privileges for next season. The 17-year-old had a closing 4-under 66 and rocketed up the leaderboard, tying for fifth at 3-under 277.