PHOENIX, 23 Mar 2015 (AFP) - The 19-year-old South Korean had seven birdies in her five-under par 67, capturing a second LPGA Tour title to go with the major crown she earned at the Evian Championship last year.
Kim led Lewis by two strokes going into the final round at Wildfire Golf Club.
Lewis closed within one shot late on Sunday but bogeyed the last to cap a four-under par 68.
Her 18-under par total of 270 gave her a second runner-up finish in her last three events.
Even though she started the day with the lead, Kim said she wasn't thinking about lifting the trophy.
"In the morning, I wasn't concentrating on winning because I was playing with Stacy Lewis and as a rookie, I just felt that by playing with her, I would learn a lot from her," Kim said.
"So I was just trying to make a good impression as a rookie."
South Korean Lee Il-Hee grabbed a share of third place with a six-under par 66. She was joined on 272 by compatriot Lee Mi-Hyang, who carded a 68, and Thailand's Pornanong Phatlum, who signed for a 67.
World number one Lydia Ko fired a three-under par 69 for the third straight day to lead a group of five players sharing sixth place on 15-under 273.
Sweden's Anna Nordqvist joined the group with a sparkling 64, American Austin Ernst and South Korea's Kim Sei-Young both posted 65s, while South Korean Choi Na-Yeon posted a 66 for 273.
After a birdie at the second, Kim gave the stroke back with a bogey at the par-three fourth, but was one-under for the round with a two-stroke lead at the turn after a birdie at the ninth.
At the 10th, her drive landed near a tree housing a beehive, but she was denied relief and ended up with a bogey.
"I wasn't frustrated or anything. If anything, I was just scared of the bees and I didn't want to be stung by them or anything like that," Kim said.
"So I kept asking if I can get relief and I kept asking and they said, 'No, you can't.'
"So I just swallowed my fears and tried to play the shot as best I could.
"If anything, I think the situation on hole 10 helped because after I went through there and I got a bogey, I just realized there's no time to feel pressure or feel afraid," she said. "I've just got to go out there and play."
Kim bounced back with a seven-foot birdie putt at the 11th then drained a long birdie putt at 12. She sank a three-footer for birdie at 13, and two-putted for birdie at 15.
Meanwhile, Lewis was keeping the pressure on.
She made back-to-back birdies at 12 and 13, then birdied 15 and 16, her four-foot effort at the 16th pulling her within one shot of Kim's lead.
After pars at 16 and 17, Kim rolled in a seven-footer for birdie at 18, her winning margin growing thanks to Lewis's bogey at the last.
"That back nine was pretty cool, the way we made birdies back and forth and on top of each other," Lewis said. "I'm proud of the way I hung in there."
Leading scores after Sunday's final round of the LPGA Founders Cup (USA unless noted, par-72):
267 - Kim Hyo-Joo (KOR) 65-69-66-67
270 - Stacy Lewis 64-71-67-68
272 - Lee Il-Hee (KOR) 69-67-70-66, Pornanong Phatlum (THA) 68-71-66-67, Lee Mi-Hyang (KOR) 70-66-68-68
273 - Anna Nordqvist (SWE) 72-67-70-64, Austin Ernst 68-67-73-65, Kim Sei-Young (KOR) 69-66-73-65, Choi Na-Yeon (KOR) 70-66-71-66, Lydia Ko (NZL) 66-69-69-69
274 - Sandra Gal (GER) 68-70-67-69, Lizette Salas 73-65-67-69
275 - Jane Park 67-72-67-69, Amy Yang (KOR) 68-69-68-70, Jang Ha-Na (KOR) 68-68-68-71, Kim Kaufman 66-67-70-72
276 - Ai Miyazato (JPN) 70-69-71-66, Baek Kyu-Jung (KOR) 69-69-71-67, Jessica Korda 72-66-71-67, Angela Stanford 67-70-71-68, Moriya Jutanugarn (THA) 67-69-70-70, Ariya Jutanugarn (THA) 69-66-70-71, Lin Xiyu (CHN) 71-66-68-71
277 - Haru Nomura (JPN) 69-70-70-68, Feng Yueer (CHN) 73-66-69-69, Jaye Marie Greene 69-70-69-69, Cheyenne Woods 70-70-67-70, Alison Lee 70-70-63-74