For Kim, the victory was her second this season and the seventh of her career. For Gulbis, the runner-up finish extended her winless drought to 123 starts on the LPGA Tour.
Gulbis, who played the front nine at 5-under-par 29, made a spectacular birdie at the 10th, then parred her final eight holes to tie Kim at 18-under-par 266 for the tournament.
Both players shot 6-under 66 in the final round -- setting up the dramatic sudden-death playoff.
Kim gave Gulbis two good chances to end the playoff on the first two extra holes -- played at the par-5 18th and 17th holes -- by hitting the rough with her drive both times.
Barely 5-feet tall, Kim struggles out of the long grass, but managed to make two pars.
Gulbis found the fairway on the first two playoff holes, then missed birdie putts of 18 feet and 12 feet -- sending the playoff back to the 18th hole for the second time.
There, both players found the rough off the tee. Kim got lucky with her second shot, just flying a creek that runs through the fairway, while Gulbis knocked hers to the center of the fairway.
After Kim landed her approach in the middle of the green, Gulbis stuck hers inside her opponent's to about 15 feet.
Kim then cooly rolled in her birdie putt. Gulbis missed hers just right.
Kim won the Ginn Clubs & Resorts Open in April and has seven other top-10 finishes this season, outside of her two victories. She claimed $180,000 for the win Sunday.
Gulbis' loss is the latest disappointing chapter in what has been a promising, yet fruitless, four-year LPGA career.
The woman with her own reality show -- and more than $2.2 million in career earnings entering this week -- was running away with the tournament early Sunday after the third round was completed in the morning.
She began the final round in a tie with Kim for the lead. Gulbis opened with back-to-back pars on her first two holes, then collected five consecutive birdies.
Gulbis went pin-seeking during her birdie spurt, knocking approaches within 12 inches at the third and within seven feet at both the fourth and the sixth holes.
Gulbis also rolled in birdie putts of 15 feet at the fifth and 12 feet at the seventh -- the last of which put her at 17 under for a four-shot lead.
But, ironically, her birdie streak ended when she actually hit a pin at the par-3 eighth. The ball landed a foot past the hole, then spun back far enough away that Gulbis settled for a par.
Kim made birdie at the eighth and ninth to get to minus-15 and within two shots. Two holes later, Gulbis nearly aced the par-3 10th on the way to another birdie.
But that's when the momentum shifted.
Kim also birdied the 10th to remain within two shots, and she had more red numbers up her sleeve. After collecting a fifth birdie with an 18-inch putt at the 16th, Kim rolled in a 10-footer for birdie at the 17th to tie Gulbis for the lead.
Gulbis hit a thin approach shot at 17 and landed short of the green in the rough. At the 18th, she missed an 18-foot birdie try after Kim couldn't convert on a 25-foot try.
Now in her fifth season, Gulbis has challenged often without a win. She had a career year in 2005, when she ranked sixth on the money list with just over $1 million, and now has six top-10 finishes this season.
Gulbis' winless drought is far from an LPGA record (Carolyn Hill went 359 starts before winning the 1994 McCall's LPGA Classic) but still -- a title eludes her.
Paula Creamer made a run at the lead, but finished one shot back at 17-under-par 267 to take third place. Creamer birdied four straight holes from the 14th and fired a 6-under 65 in her final round.
Se Ri Pak, a four-time winner here, shot a 5-under 66 in her final round and finished in fourth place at minus-16. Reilley Rankin was fifth at 12 under, and Brittany Lang and Sung Ah Yim shared sixth one shot further back.
World No. 1 Annika Sorenstam closed with a 1-under 70 in her final round and took eighth place at minus-9.