KOHLER, Wisconsin, July 8, 2012 (AFP) - Choi, 24, fired a one-over 73 at Blackwolf Run for a seven-under total of 281 and a four-shot victory over another South Korean, Amy Yang.
Choi had gone into the final round with a six-shot lead thanks to a remarkable 65 in Saturday's wind-whipped third round.
Yang carded a one-under 71 for a three-under total of 285, with no other players finishing under par for the event.
Choi's triumph came on the same course where Se Ri Pak won the 1998 US Women's Open, a victory Choi recalls watching on television as a girl.
Pak was among the players who rushed out to spray Choi with champagne and hug her after the last putt dropped at 18.
Despite the big lead she took into the round, Choi had plenty of work to do on Sunday, especially after a triple-bogey eight at the par-five 10th hole.
Her tee shot was left into deep rough and after she was unable to find her ball she returned to the 10th tee.
Yang, meanwhile, parred the hole to cut the deficit to two shots.
Choi bounced back with a birdie at 11, but was in trouble again at 12, where her approach shot ended up in tall, dry grass short of the green.
She chipped out and found the green, rolling in a 20-footer to save par.
At 13 she had a narrow escape when her tee shot headed toward the water but along the rocks and stayed dry.
She picked up birdies at 15 and 16 to regain control.
Choi, who came into the tournament ranked fifth in the world, claimed her sixth LPGA title and her first major.
Until Sunday, Choi had eight major top-10 finishes, including a tie for second at the US Women's Open in 2010.
She became the fourth South Korean to win the event in the past five years, following Inbee Park in 2008, Eun-Hee Ji in 2009 and So Yeon Ryu last year.
Germany's Sandra Gal carded a 74 on Sunday to finish third on one-over 289.
Il Hee Lee of South Korea, Feng Shanshan of China and Italian Giulia Sergas were tied on two-over.
World number one Yani Tseng of Taiwan couldn't get her game going all week and finished 14-over. She remains in search of a US Women's Open win to complete her career Grand Slam.
Leading final-round scores on Sunday in the US Women's Open (USA unless noted, par 72):
281 - Na Yeon Choi (KOR) 71-72-65-73
285 - Amy Yang (KOR) 73-72-69-71
289 - Sandra Gal (GER) 71-70-74-74
290 - Ilhee Lee (KOR) 72-71-77-70, Feng Shanshan (CHN) 74-74-71-71, Giulia Sergas (ITA) 74-71-73-72
291 - Paula Creamer 73-73-71-74, Mika Miyazato (JPN) 71-71-73-76
292 - Se Ri Pak (KOR) 72-73-76-71, Nicole Castrale 73-70-74-75, Inbee Park (KOR) 71-70-76-75, Cristie Kerr 69-71-77-75, Suzann Pettersen (NOR) 71-68-78-75
293 - Cindy Lacrosse 73-74-74-72, Danielle Kang 78-70-71-74, So Yeon Ryu (KOR) 74-71-74-74, Lexi Thompson 70-73-72-78
294 - Hee Kyung Seo (KOR) 72-73-80-69, Brittany Lincicome 69-80-74-71, Vicky Hurst 71-70-75-78
295 - Yeon-Ju Jung (KOR) 74-72-80-69, Diana Luna (ITA) 76-72-76-71, Brittany Lang 73-74-77-71, Jennie Lee 70-74-79-72, Numa Gulyanamitta (THA) 73-76-73-73
Jimin Kang (KOR) 72-72-78-73, Azahara Munoz (ESP) 73-73-73-76
296 - Anna Nordqvist (SWE) 72-74-79-71, Mina Harigae 77-71-75-73, Pornanong Phatlum (THA) 76-69-76-75, Ai Miyazato (JPN) 70-74-75-77
297 - Sun Young Yoo (KOR) 76-72-81-68, Jin Young Pak (KOR) 73-72-80-72, Lizette Salas 69-73-75-80