The 25-year-old ran away with victory via a crucial birdie that she managed to sink from an awkward spot on the green, before taking an even par on the final hole to card a two-under 70 on the last day of the season-ending tournament.
That birdie followed two earlier and an eagle on the par-five fifth hole as she regained composure after a double-bogey at the third.
The win is Choi’s second this year and supplements an outstanding 2012 LPGA campaign during which she also US Women's Open, was worth $500,000 and took her total prize money for the season to $1.9 million.
Ryu was tied for the lead with Choi for the first 13 holes, until a three-putt bogey on the 14th relegated her to second, the position she stayed for the rest of the round.
The Rookie of the Year award winner finished with a 70 for 276.
Inbee Park won the money title and the Vare Trophy for lowest scoring average.