It was the fourth professional win for Day but the first in his native Australia. It also comes about a week after Day learned that eight family members were among those killed in the Philippines by Typhoon Haiyan.
Day won the individual title at the World Cup of Golf by two strokes over Thomas Bjorn. World No. 2-ranked Adam Scott was third, giving Australia the team championship by 10 strokes over the United States.
Day moves to 11th in the world rankings with a rankings point average of 5.35, right behind 10th-ranked Jason Dufner (5.38).
Scott's showing slightly narrowed the gap between him and world No. 1 Tiger Woods, who has been atop the rankings for a total of 658 weeks.
Luke Donald, who was second in the rankings at the end of 2012, defended his Japan Tour's title in Miyazaki, Japan. That moves him from 17th to No. 15 in the current rankings.
Morten Orum Madsen claimed his first European Tour title by winning the South African Open Championship and improves his standing 123 spots to No. 121 in the rankings.
The men's world golf Top 10, listing player's name, home country and rankings point average:
1. Tiger Woods, United States, 12.11
2. Adam Scott Australia, 9.80
3. Henrik Stenson, Sweden, 8.94
4. Phil Mickelson, United States, 7.70
5. Justin Rose, England, 7.63
6. Rory McIlroy, Northern Ireland, 6.51
7. Matt Kuchar, United States, 6.38
8. Steve Stricker, United States, 6.13
9. Brandt Snedeker, United States, 5.74
10. Jason Dufner, United States, 5.38