The format of the tournament changed for this year's event, making it an individual contest with the team aspect being secondary. Day also won that component alongside countryman Scott. The pair combined to finish 17 strokes under par.
As Dennis Passa of the Associated Press (via ABC News) points out, it was the first tournament in five weeks for Day, who lost relatives in this month's typhoon in the Philippines:
The World Cup was Day's first tournament in five weeks and came two weeks after he learned that eight of his relatives, including his grandmother, died in the Nov. 9 typhoon in the Philippines.
His mother, who migrated to Australia from the Philippines 30 years ago, and sister were just off the green on 18. They both hugged him as he walked to the scoring tent to sign his card.
Day took to Twitter after the win to thank fans for their support:
At 10 under par, the Australian won the event by two strokes over Bjorn and three strokes over Scott, who made a charge in the final round but couldn't catch his partner for the individual title.
Even though Day has been a constant presence near the top of the leaderboard, especially during majors, the win in Melbourne marks his first victory since the HP Byron Nelson Championship in 2010. His only other win came at the Nationwide Tour's Legend Financial Group Classic in 2007.
The strong showing could bode well for the 26-year-old. His ability to compete at a high level in major tournaments was always a positive sign, but if he can start turning those close calls into wins, he can become one of the best players in the world.
Coming out on top in the World Cup of Golf is a step in the right direction for Day, but bigger wins are likely on the horizon.