MELBOURNE, November 24, 2013 (AFP) - He combined with reigning US Masters champion Adam Scott in storming to "team" victory by a massive 10 shots over the United States, claiming an Australian success for the first time since Wayne Grady and Peter Fowler captured the title in 1989 in Spain.
The Filipino-Australian also won the individual honour along with a $US1.2 million first prize cheque in posting a final round 70 to defeat Denmark's Thomas Bjorn by two shots with a 10-under par tally.
The 27-year-old started the final round one shot ahead of Bjorn and despite a bogey at the first, he was never behind after holing a 95-yard wedge shot for eagle at the par four, sixth hole.
It was Day's first victory on home soil since turning professional in 2006 and it came just days after learning his grandmother, uncle and six cousins were among thousands killed by Typhoon Haiyan which struck the Philippines on November 8.
"It feels great to win in Australia for a first time but then I really don't know what to think about right now," said Day, whose Filippino-born mother Dening and sisters broke into tears in witnessing his triumph.
"All the hard work and dedication I have put into my game, especially over the last five to 10 years when I have really taken it seriously, is paying off.
"It has taken me a while to get my second wind and it just seems fitting to have Scotty by my side and for the two of us to share victory in the World Cup down here in Melbourne.
"Even though it was very difficult conditions again today out there, it was a lot of fun, and today I learnt a lot about myself and I am just really excited for next week to get started, as well."
Scott commenced his round in brilliant fashion, holing a 120-yard wedge shot for eagle at the first and birding his next two holes to continue his scintillating form having won the the Australian PGA and Australian Masters already this month.
Both Day and Scott now head to Sydney for Thursday's Australian Open where Scott will be looking to become only the second player in the history of Australian golf to win the "Australian Grand Slam" -- winning all three main Australian events in the same year.
"I now have to get myself ready for the Australian Open and it's something that means so much to all the Australian golfers, and at a great venue like Royal Sydney," he said.
"I am looking forward to the challenge and obviously Jason is playing great, while there is a host of other players who would badly love to win this coming week.
"So I am going to have my work cut out."
Despite Scott's third place individual finish, he will remain in second place on the World Rankings behind 14-time Major winning Tiger Woods.
Bjorn had led after two rounds with a pair of 68s but could manage no better than a pair of 71s over the weekend, but the Dane was gracious in defeat.
"Naturally, I am a fraction disappointed but I just didn't play great today," he said.
"I couldn't be happier for Jason. He has gone through a rough time of late and for him to even be here is a big thing and then to go and go and win the golf tournament, and for him to also win the team event, is fantastic."
Final-round scores on Sunday at the World Cup of Golf at Royal Melbourne:
INDIVIDUAL
274 - Jason Day (AUS) 68-70-66-70 276 - Thomas Bjorn (DEN) 66-68-71-71 277 - Adam Scott (AUS) - 75-68-68-66 278 - Matt Kuchar (USA) 71-68-68-71 281 - Ryo Ishikawa (JPN) 71-71-70-69, Kiradech Aphibarnrat (THA) 71-70-70-70 282 - Hideto Tanihara (JPN) 72-67-71-72 283 - David Hearn (CAN) 70-71-71-71, Stuart Manley (WAL) 67-72-72-72, Kevin Streelman (USA) 66-69-74-74, Francesco Molinari (ITA) 75-67-66-75
284 - Brendan De Jonge (ZIM) 74-72-70-68, Maximillian Kieffter (GER) 73-71-70-70, Bernd Weisberger (AUT) 71-72-69-72 285 - Roope Kakko (FIN) 72-72-69-72, Gregory Bourdy (FRA) 72-69-72-72, K J Choi (KOR) 67-74-71-73, Ricardo Santos (POR) 69-69-73-74, Graeme McDowell (NIR) 72-71-67-75
TEAM
551 - Australia (Day/Scott) 561 - United States (Kuchar/Streelman) 563 - Japan (Ishikawa/Tanihara), Denmark (Bjorn/Olesen) 570 - Canada (Hearn/Fritsch) 572 - South Africa (Coetzee/Grace) 573 - Germany (Siem/Kieffer), France (Bourdy/Dubuisson)