LANCASTER, Pa. >> In Gee Chun’s modest goal for her first U.S. Women’s Open was to enjoy every new experience.

Boy, did she enjoy herself.

The 20-year-old South Korean stormed from behind, posting birdies on four of the last seven holes to rally for an unlikely one-stroke victory Sunday.

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.

“Everything I faced and I did here was completely new,” Chun said. “So all I did was enjoy the new stuff … I enjoyed it and had a lot of fun. Even though I’m Korean, here American fans supported me a lot and they gave a lot of claps. That has put me in the great rhythm of play, and I enjoyed that tournament rhythm.”

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. Lewis was three back at the start of the round.

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

Wie had three bogeys on the front nine for a 38 to fall back. But she rallied for two birdies and an eagle to offset one bogey on the back nine to close with a 32. Wie earned $100,542.

Punahou senior Mariel Galdiano, an amateur, shot a final-round 71 to finish tied 42nd at 286.