Then it was Ai Miyazato's turn to misfire, sending a shot on the 18th hole into the water. Choi hit her approach to within five feet, sank the birdie putt and went on to celebrate her first LPGA Tour win.
Just how she planned it, right?
"I can't believe that I won," Choi said. "Throughout the second half I thought I was going to lose it again."
The South Korean's up-and-down round Sunday resulted in a 1-under 71 that was good enough to take the Samsung World Championship.
Miyazato, of Japan, finished with a 69 for a low round of the day that wasn't good enough to best Choi's 16-under 272.
Choi began the final round with a two-stroke lead, got birdies on two of her first four holes and made a 10-foot eagle putt on the sixth hole to extend her lead to seven strokes.
It looked then as if Choi, who has won four times on the Korean LPGA Tour, would cruise to a win.
But Miyazato, playing in the group in front of Choi and Jiyai Shin of South Korea, made two quick birdies on Nos. 7 and 8 to cut Choi's lead to five.
"I played really good," Miyazato said. "I was very patient."
Choi missed a 2-foot putt on the ninth hole for a bogey, cutting the lead to four heading into the back nine.
She continued to struggle with two consecutive bogeys, and Miyazato tied Choi at 16-under with a 4-foot birdie putt on No. 16.
Miyazato took the lead shortly after, when Choi three-putted for bogey on No. 14.
Choi has been working with a sports psychologist on her mental game and was repeating some of the lessons she has recently learned.
"Mentally, I felt I was very weak," Choi said. "I kept telling myself to be positive. I wanted to be positive about everything."
On the 18th hole, it was Miyazato's turn to make a mistake. With 203 yards remaining for her second shot, Miyazato's 5-wood approach hit the bank in front of the 18th green and rolled into the water. She dropped in front of the pond but could not get up and down for par.
Choi's second shot on the 18th reached the front left of the green and her third shot came to rest 5 feet below the pin. Choi, who had missed several putts of equal or less distance, converted the birdie for the victory - no easy task.
"I felt like I had just turned professional today," Choi said when facing the putt for victory. "I was so nervous."