South Korea's In Gee Chun storms from behind to win US Women's Open in championship debut

In Gee Chun hits an approach shot off the 13th fairway during the final round of the U.S. Women's Open golf tournament at Lancaster Country Club, Sunday, July 12, 2015 in Lancaster, Pa. (AP Photo/Gene J. Puskar) (The Associated Press)

In Gee Chun reacts after sinking a putt for birdie on the 15th green during the final round of the U.S. Women's Open golf tournament at Lancaster Country Club, Sunday, July 12, 2015 in Lancaster, Pa. (AP Photo/Frank Franklin II) (The Associated Press)

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.

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 was second at 273.