Il Mi Chung holed out for eagle at the 14th, en route to a 7-under 65. She finished as the medalist at 9-under-par 207, one shot better than Julieta Granada (69) and Mi Hyun Kim (65).
The final three to get into the final round shared sixth at minus-4.
Player of the Year Lorena Ochoa (67), Paula Creamer (70) and Natalie Gulbis (72) earned the final spots on Sunday.
Not that the 54-hole scores mean anything.
In the first year of this season-ending event, the scores for the eight players who advanced to the final round are wiped out. Essentially, it's a shootout on Sunday and the lowest score wins and pockets an LPGA Tour record $1 million.
'It's such an interesting format,' acknowledged Gulbis, who could make her first LPGA Tour victory a very lucrative one. 'It's been fun and really exciting.'
Gulbis was the last player to secure her spot. She was 1 under par through her first seven holes, but back-to-back bogeys at eight and nine almost cost her a spot in the final round.
Gulbis failed to get anything going through the five holes of her second nine, but a 10-foot birdie putt at the 15th got her to 4 under par, inside the bubble.
At both the 16th and 17th holes, Gulbis had good birdie looks that could solidify her place on Sunday. She missed both and needed a par or better to avoid a playoff with Jeong Jang for the final spot.
Gulbis hammered her drive over the water at the closing hole at Trump International safely finding the fairway. She knocked her second just short of the green, but got a great bounce and rolled to 12 feet. Gulbis lagged her birdie try, then tapped in for her berth in the final round.
'I knew at the turn that I needed a couple of birdies coming in,' said Gulbis. 'I'm a leaderboard watcher.'
Creamer also went through a little anxiety before earning her spot. Last year's LPGA Tour Rookie of the Year made the turn at 1 under par, but a bogey at the 11th knocked her outside the top eight.
Creamer holed a putt from just off the green at the par-4 13th to reach 3 under par. She was still outside the mark, but one more birdie would get her in, or all pars could mean a playoff.
She waited until the last hole to cement her status. Creamer landed in the short grass off the tee, then hit a spectacular approach to 3 feet. She rolled in the putt and advanced to Sunday.
'I've always said I like playing under pressure,' said Creamer. 'That was a big shot and I'll try to have the same attitude as today. It will be an interesting Sunday.'
Chung cruised along with four birdies through her first 11 holes, including three in a row from the second. It was her spectacular approach at the 14th that got her in position for medalist honors.
Chung hit her second left of the flag, but the ball took the slope and rolled in from almost 25 feet. The eagle put her at minus-8, then a birdie at the last moved her one ahead.
Jang was the closest to moving into Sunday's final round, but a 2-under 70 n Saturday left her one shy of the number.
Diana D'Alessio (72), Juli Inkster (70) and Cristie Kerr (71) finished at 1-under-par 215. Hee-Won Han (73) and Se Ri Pak (75) tied at 1-over-par 217.
Morgan Pressel struggled to a 3-over-par 75 to finish at 4-over-par 220. Wendy Ward was even worse with an 11-over 83 and came in at 8-over-par 224.
The field started at 32, but was cut to 16 after Friday's second round. Inkster, Pressel and Ochoa survived the six-player extra session. Brittany Lang, Pat Hurst and Jee Young Lee were knocked out.
Annika Sorenstam, who won the last two titles at the ADT Championship, went 74-72 and missed the cut.