Higher up the leaderboard, Thai star Jutanugarn snatched victory from the jaws of defeat with birdies on the 17th and 18th holes to earn an overall 15-under.
American rival Lexi Thompson had earlier bogeyed her 18th hole to fall to 14-under par and give Jutanugarn a sniff of victory, upon which she pounced.
Jessica Korda also finished on 14-under par. It was Jutanugarn's seventh LPGA tour event win.
Nevertheless, Thompson took home the season-long Race to the CME Globe title and its $US1 million ($NZ1.4m) reward as the tour's leading points earner.
Ko remained in the running for the title until this week's season-ending event, but needed to win and hope other golfers faltered.
Elsewhere, male compatriot Ryan Fox finished in a tie for 28th in the European Tour's World Tour Championship in Dubai with an overall eight-under.
He was 11 shots off Spanish winner Jon Rahm.
- AAP