Leishman won twice earlier this year and gave himself a shot at another trophy with a birdie on the 72nd hole to join Justin Thomas in a playoff in South Korea.
While both men parred the first extra hole, Leishman was the first to blink when he sailed his approach to the par-5 18th hole into the water.
Leishman was making his first stroke-play start of the new season, coming off a career campaign that included wins at the Arnold Palmer Invitational and BMW Championship.
