Justin Rose became world number one on Monday despite he lost a playoff against American Keegan Bradley at the BMW Championship in suburban Philadelphia.
Rose got a lucky break in the playoff when his approach shot landed in a skybox but ricocheted back towards the hole and stopped just off the green.
However he misjudged his putt through the soggy grass, and it came up well short of the hole before he missed the par putt.
That left Bradley to tap in for the win.
Justin Rose pumps his fist after a birdie on the 16th hole during the final round of the BMW Championship on September 10, 2018. /VCG Photo
The disappointment of not winning the tournament was eased by Rose's rise to the top of the rankings for the first time, where he surpassed American Dustin Johnson.
"That's an amazing achievement, something I'm extraordinarily proud of," the Englishman said in a greenside interview after becoming the 22nd man to hold the top spot since the rankings began in 1986, "I would love to have got there by winning..."
Rose has won nine times on the PGA Tour, where he mostly plays, including one major, the 2013 US Open. The 38-year-old is also the Olympic gold medalist from Rio 2016.
The BMW was the third of four FedExCup playoff events on the PGA Tour.
The top 30 on season-long points list advance to the Tour Championship in Atlanta starting on Thursday week.
Rose will be one of the leaders on the European team to play the United States at the Ryder Cup in Paris later this month.