The 29-year-old sits proudly at the top of the standings but is under threat from a couple of players this week in California.
Both Dustin Johnson and Hideki Matsuyama can reach the top of the rankings for the first time on Sunday, with Johnson needing to win the event and Day to finish worse than a three-way tie for third to claim top spot.
A win for Matsuyama would make him the first male Japanese player to become world number one, should Day finishes lower than a two-way tie for 24th.
Australia's Day has been top dog for some time now and has seen Jordan Spieth's challenge fade until he won last week, while Rory McIlroy is still out injured.
There are new challengers this week and Day is just happy to do his thing and let the rest take care of itself.
"I said earlier that to be number one for a calendar year would be great, but I need to just focus on what I need to do because you can't really focus on staying number one," he said.
"The more you focus on the actual target itself, the more you attach yourself to it, you make mental errors out there, you get more frustrated, you do silly things on the golf course that you shouldn't be doing.
"I need to focus on hitting the shot in front of me, going to the next shot and hitting that and trying to beat everyone else because I know that as long as I win, it will take care of it.
"If someone takes it off me, I'm okay with it. I'm not going to be angry or sad about it. Just goes to show that I need to work harder, need to be smarter and try and win more tournaments."