Jason Day replaced Rory McIlroy as world number one after winning the BMW Championship by six shots in Chicago.
The Australian, 27, finished with a birdie as he carded a two-under 69 to triumph on 22 under par.
Daniel Berger of the United States was second after a two-under 69, one ahead of compatriot Scott Piercy (70).
Northern Ireland's McIlroy finished with a 70 to tie for fourth on 14 under with Americans JB Holmes and Rickie Fowler, eight shots adrift of Day.
Day admitted to nerves ahead of his bid to go to the top of the world rankings, saying: "To be honest I had terrible sleep over the last few nights.
"Thinking about getting to number one, thinking about winning this tournament, thinking what I had to do to win this tournament to get to number one."
He added: "Just to play the way I did, very disciplined, knowing that I had to be patient, not looking at leaderboards as much....I felt like I did it pretty good today."