Rory McIlroy has been bumped off the world number one spot after the BMW Championship in Chicago.
Australian golfer Jason Day clinched the title as he dominated the tournament on Sunday at Conway Farms.
Last week McIlroy took the top spot back from Jordan Spieth marking the fourth consecutive week the pair traded places at the top.
However it was 27-year-old Day who succeeded Rory McIlroy at the top of the rankings after a final round of 69 earned him a six-shot victory at the BWM Championship.
The US PGA Championship winner admitted it hadn't sunk in just yet.
"I'm not really thinking about it right now. It doesn't feel real," he told Sky Sports 4.
"Knowing the Shark (Norman) spent 331 weeks up the top of the world ranking list - a very long time - and next week's going to be my first week."
The 27-year-old Australian added: "I feel good. Just all the work ever since I was a little kid trying to get to number one in the world and today I did it, which was great.
"To have an opportunity, knowing I had to win this week to gain that spot, and stepping up and doing it was fantastic."
Day begins his reign as World Number One by playing at The Tour Championship which starts on Thursday.
He said: "I'm going to take Monday and Tuesday off.
"I'm going to go home (to Westerville, Ohio) and then I'll fly down to Atlanta on Tuesday night. Try to get as much rest as possible. The last two days have been very stressful for me.
"Emotionally it's been very up and down inside. I may not show it but inside I'm going up and down.
"I've got to try to reset everything. After this week, after my celebration tonight, it's done. I've got to get into next week and try to win the FedEx Cup."