Last year, Day also reached the semi finals where he was eliminated by eventual winner Matt Kuchar before beating Ian Poulter in the consolation match for third and 4th.
If Day defeats his semi final opponent, Rickie Fowler tomorrow he will be guaranteed a rise to 6th in the world ranking and if he was to go on and win his second PGA Tour title on Sunday afternoon he would rise to an all time high of 4th in the world.
Fowler defeated Jim Furyk 1 up in a tightly fought match.
In the other semi final Ernie Els takes on surprise packet Frenchman Victor Dubuisson after Dubuisson had fought back from an early deficit to defeat Graeme McDowell 1 up, McDowell unable to produced another Houdini act after producing miraculous fight-backs in earlier matches.
Els defeated Jordan Spieth 4&2.
The winner of tomorrow's final earns US$1,530,000. although just for making it to the semis, Day is guaranteed more than US$500,000, more then $630,000 for 3rd and if he makes the final he is assured of $US900,000.