Ko fired a final round even-par 72 to finish at 11-under for the tournament.
Closest rival Inbee Park finished one stroke ahead but it wasn't enough to deny Ko the world number one status and the Rolex player of the year title for the first time.
Ko was in tears following her round as the accomplishment dawned on her but said he putting let her down today.
"I think the hole was smaller than the ball today, a lot of lip outs and a lot of close ones, but they just weren't dropping."
"It was the same case yesterday."
The US$1m payout for the season-long Race to the CME Globe title takes Ko's earnings for 2015 past US$3m and tops US$5m for her career.
It is Ko's 17th top 10 finish of the year in 24 tournaments, in which five were victories.
American Christie Kerr won the event for her second victory of the year after a four-under 68 saw her finish at 17-under, a shot ahead of South Korea's Ha Na Jang and compatriot Gerina Piller.
