Her 31-under total of 257 broke the LPGA's 72-hole scoring record in relation to par of 27-under, first set by Swedish great Annika Sorenstam in 2001 and matched by Kim herself at the 2016 Founders Cup in Phoenix.
Kim shot her previous record-equaling effort of 27 under at the 2016 Founders Cup, drawing her level with her childhood hero Sorenstam.
"I feel like this is the best I've ever played", said Kim, who matched the LPGA's 54-hole scoring record of 24-under set by Annika Sorenstam at the 2003 Mizuno Classic - now known as the Toto Japan Classic.
"Just before starting (Sunday), I was just setting my goal as a bogey-free round", Kim said. "I did today, so I'm very happy with another good round". But after the major tournament, I realized, 'OK, I can do that.' If I imagine, it comes true.
Even with an eight shot lead entering the round, Kim never let her foot off the gas pedal.
The second-place finish went to Carlota Ciganda, who ended nine strokes adrift of Kim, while Anna Nordqvist, Emma Talley and Amy Yang tied for third. Hee Young Park won a playoff after she and Angela Stanford each finished at 258 in the Manulife Classic in Canada in 2013 (par 71), while Karen Stupples shot 258 at the Welch's/Fry's Championship in Arizona in 2004 (par 70). Ciganda missed the fairway and wound up with an unfortunate double bogey cut she still closed with a final round 64 to claim sole possession of 2nd at -22. She had 31 birdies and one eagle, another record for most sub-par holes in a tournament. It's pretty exciting to watch, really.
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"In a word, phenomenal", Kirk said of Kim's performance. "It's unbelievable the way she (Sei Young) played".
Ayako Uehara, who birdied seven times and opened three shots off the pace with a 65 on Thursday, carded a final-round 69 and finished tied for 47th at 278. Kim required just 115 putts over the 72 holes.
Sei Young Kim won't only be chasing a victory at the Thornberry Creek LPGA Classic on Sunday.
She was ranked as high as number eight in the world a year ago after her win in Mexico and has struggled for much of 2018. Over the four rounds, Kim had one eagle, 31 birdies and one double bogey but did not have a single bogey.
"First hole, my second shot was nearly a tap-in birdie, so (I) started really solid", said Kim, who is seeking a seventh LPGA title.
The win was the seventh of Kim's LPGA career, her first since she captured the Lorena Ochoa Match Play in May 2017.