SAN FRANCISCO, April 28, 2014 (AFP) - Three days after her 17th birthday, the South Korean-born Kiwi fired a final-round three-under par 69 to finish 72 holes on 12-under 276 to win the inaugural $1.8 million event at Lake Merced in California.
It completed a landmark week for Ko, who pocketed $270,000 and was named to Time magazine's list of the world's 100 most influential people on Thursday, the only golfer so honored.
After a bogey at the fourth, she began a run of three birdies in four holes at the par-5 sixth, although she had bogeys at seven and 10 to keep her in a pack battling for the lead.
Ko made back-to-back birdies at the 13th and par-5 14th to reach 11-under and lead by two. American Lewis birdied the 16th and South Korean Jenny Shin, who finished third on 278, birdied 17 to move within one stroke on the last tee.
Shin settled for a par at 18 and third place while Lewis birdied the par-5 finishing hole, but so did Ko to take the victory over a field that featured 18 of the 20 top-ranked women in the world.
Ko, ranked fourth, collected her third LPGA title and first US triumph. She won the 2012 and 2013 LPGA Canadian Women's Open titles as an amateur, triumphs that helped convince the women's tour to waive their 18-year-old age minimum in her case.
World number one Park In-Bee of South Korea, China's Feng Shanshan and Denmark's Line Vedel shared fourth on 282.
Scores on Sunday after the final round of the $1.8 million Swinging Skirts LPGA Classic (par 72, USA unless noted):
276 - Lydia Ko (NZL) 68-71-68-69
277 - Stacy Lewis 69-69-68-71
278 - Jenny Shin (KOR) 68-74-68-68
282 - Park In-Bee (KOR) 73-68-73-68, Line Vedel (DEN) 72-71-70-69, Feng Shanshan (CHN) 74-70-68-70
284 - Kim Hyo-Joo (KOR) 69-73-72-70, PK Kongkraphan (THA) 74-68-70-72
286 - Cristie Kerr 73-75-70-68, Michelle Wie 72-72-71-71, Brittany Lang 71-71-72-72, Karine Icher (FRA) 66-73-73-74
287 - IK Kim (KOR) 72-71-72-72, Haeji Kang (KOR) 72-70-72-73
288 - Azahara Munoz (ESP) 76-69-73-70, Ji Eun-Hee (KOR) 73-71-74-70, Ashleigh Simon (RSA) 73-70-73-72
289 - Caroline Masson (GER) 74-75-72-68, Yoo Sun-Young (KOR) 72-76-69-72, Park Hee-Young (KOR) 70-73-68-78
290 - Mina Harigae 75-73-73-69, Haru Nomura (JPN) 75-73-71-71, Alison Walshe 74-69-76-71, Mika Miyazato (JPN) 72-69-77-72, Lee Il-Hee (KOR) 68-73-76-73, Catriona Matthew (SCO) 73-69-74-74, Pornanong Phatlum (THA) 72-72-71-75
291 - Lee Mi-Hyang (KOR) 72-76-74-69, Suzann Pettersen (NOR) 70-72-79-70