Both players recorded pars on the first playoff hole, but it was a different story on the second as Ko hit a birdie to seal the deal, while Pressel could only manage another par.
The playoff was set up after Ko hit a 70 in her final round, which included six birdies and four bogeys, while Pressel carded a 72, which consisted of two birdies, four bogeys and an eagle on the par-five 6th.
Overnight leader Brooke Henderson finished third after she hit one birdie, five bogeys and an eagle on the par-five 14th during her final round 74.
South Korea's Min Seo Kwak finished one stroke behind Henderson as she too recorded a final round 74, which included two birdies and four bogeys, three of which came in a row on the 6th to 8th hole.
Meanwhile, world number two Inbee Park ended up tied in 18th place on the leaderboard after she sunk two birdies and two bogeys during her final round 72.