LANCASTER, 12 Jul 2015 (AFP) - World number 20 Chun, the leading money winner on the South Korean tour, fired a final round four-under par 66 to win a back-nine shootout at Lancaster Country Club for her first major title after 15th-ranked compatriot Amy Yang took a bogey on the final hole.
Chun birdied the 15th to seize the lead and the 16th and 17th to stay on top but she made bogey at 18 to open the door for Yang, who eagled 16 and birdied 17 but missed her chance with a bogey at 18.
"It was my first time playing the US Women's Open so I tried to enjoy the game in every moment," Chun said. "That led to me winning the championship."
Chun finished on eight-under 272 while Yang was second after a closing 71. World number one Park In-Bee of South Korea and American Stacy Lewis shared third on 275.
"Right off the first tee, you could feel the energy," Lewis said. "You had to fight your way through it."
Canadian teen Brooke Henderson shared fifth on 277 in a pack with Sweden's Pernilla Lindberg, Japan's Shiho Oyama, South Korean Ryu So-Yeon and Americans Morgan Pressel and Jane Park.
Chun became the third-youngest winner in US Women's Open history after Park, who won in 2008 at age 19, and Pak Se-Ri, who was 20 when she won the 1998 crown. She was the first player to win the event in her debut since compatriot Birdie Kim a decade ago.
"It was great. I tried to have fun. Every moment was new," Chun said through a translator. "I feel the support from all Korean people right now."
Yang missed out on her first major title after topping the leaderboard for the second year in a row. She was in the final pairing on Sunday for the fourth time in five years, but it was Chun who became the sixth South Korean winner in eight years at the event.
Yang led Chun by two at the turn and three after Chun made bogey at 10.
But Yang missed the green with her approach at 11 and took a bogey, while Chun birdied 12 to pull within one and Lewis birdied 13 to join her on six-under.
When Yang took a bogey at 14, she fell into a three-way tie for the lead with Chun and Lewis.
Chun jumped into the lead at seven-under with a six-foot birdie putt at 15, only the third birdie of the day at the hole, while Yang followed with a bogey at 15 and Lewis fell two back with a double bogey at 15.
When Chun sank a 14-foot birdie putt moments later at the 16th, she surged to a three-stroke edge over Yang.
Yang sank an 11-foot eagle putt at the par-4 16th to pull within one, but seconds later Chun sank a six-foot birdie putt at 17 to move two ahead.
Yang, 25, followed with an eight-foot birdie at 17 and Chun missed a 12-foot par putt at 18 to give Yang a chance.
But Yang's final tee shot went into the left rough and she missed her own 12-footer for par to hand Chun the victory.
Leading scores on Sunday after the final round of the US Women's Open (par-70, USA unless noted):
272 - Chun In-Gee (KOR) 68-70-68-66
273 - Amy Yang (KOR) 67-66-69-71
275 - Park In-Bee (KOR) 68-70-70-67, Stacy Lewis 69-67-69-70
277 - Brooke Henderson 70-73-68-66, Pernilla Lindberg (SWE) 70-70-70-67, Ryu So-Yeon (KOR) 72-68-70-67, Jane Park 66-72-71-68, Morgan Pressel 68-70-71-68, Shiho Oyama (JPN) 70-66-71-70
278 - Michelle Wie 72-68-68-70
279 - Lydia Ko (NZL) 70-72-69-68, Min Lee (TPE) 71-68-70-70
280 - Lizette Salas 71-69-72-68, Brittany Lang 70-70-72-68, Karrie Webb (AUS) 66-72-73-69, Rumi Yoshiba (JPN) 70-68-72-70, Lee Mi-Hyang (KOR) 68-72-68-72
281 - Jenny Shin (KOR) 74-68-69-70
282 - Ayako Uehara (JPN) 71-70-73-68, Lee Lopez 71-70-72-69, Marina Alex 66-71-74-71, Sydnee Michaels 68-74-69-71, Ryann O'Toole 71-70-69-72, Chella Choi (KOR) 71-73-64-74
283 - Alison Lee 70-73-74-66, Jaye Marie Green 71-73-72-67, Jang Ha-Na (KOR) 72-72-71-68, Angela Stanford 71-69-72-71, Choi Na-Yeon (KOR) 67-74-70-72, Kris Tamulis 72-69-69-73