Day was never behind in his match going 1 up at the first and although he lost the second he would win the third with a par and remain ahead for the rest of his match eventually winning with a bidie at the 17th.
Day is playing this event for just the fourth occasion, reaching the Round of 16 in 2011, the second round in 2012 and last year lost his semi final but finished 3rd after defeating Ian Poulter in the consolation match for 3rd and 4th.
Tomorrow Day will face Louis Oosthuizen after the South African comfortably accounted for Webb Simpson in his match.
If Day was to go on and win this week he would become the world's number four ranked player meaning Australia could boast two of the leading four players in the game statistically.
Other winners include Jordan Spieth who defeated the defending champion Matt Kuchar and will now face Ernie Els in one quarter final match after the South African accounted for Jason Dufner.
Jim Furyk will take on Rickie Fowler after Furyk defeated Harris English and Fowler came from three down to defeat Sergio Garcia.
In the remaining quarter final Frenchman Victor Dubuisson will face Graeme McDowell after the Accenture debutante, Dubuisson, defeated Bubba Watson and McDowell, once again, somehow snatched victory from the jaws of defeat against Hunter Mahan.