Thursday, 14 September 2017: World No.1 Dustin Johnson has been grouped with FedEx Cup frontrunners Jordan Spieth and Justin Thomas for the opening rounds of the BMW Championship.

The BMW Championship has promised a showdown between the big guns, with world No.1 Dustin Johnson grouped with Justin Thomas and Jordan Spieth for the opening two rounds.

With two runner-up finishes in his past two starts, Spieth narrowly leads the FedEx Cup standings over Thomas and Johnson, who have won the opening two events of the US PGA Tour's playoffs series between them.

With the BMW deciding the all-important top-five seedings for next week's Tour Championship finale, the stage is set for a thriller at Conway Farms Golf Club in Chicago.

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The marquee trio has intensified their rivalry during the $US67 million ($A84 million) playoffs. Big-hitting Johnson edged world No.2 Spieth in extra holes at the Northern Trust, while Thomas earned his fifth win of the season two weeks ago at TPC Boston.

Spieth, who won the British Open in July, is gunning for his second $US10 million FedEx Cup payday after claiming the 2015 series.

"I'm in a great position and looking to stay in the No.1 spot. That's my best chance to win the FedExCup and I've been through this process before, which helps," Spieth said.

World No.4 Thomas said his breakthrough major victory at the US PGA Championship in August was fuelled by ongoing comparisons to childhood friend and three-time major winner Spieth.

"The (desire) to be known as a major champion, I was driven to do it because Jordan did it. You want to keep up with your buddies and you want to win if they have more wins than you," Thomas said.

Johnson, after earning his second BMW Championship title last year, says the FedEx Cup is the biggest trophy missing from his cabinet.

"Well, I've won a major but I haven't won the FedEx Cup; it is something that I want on my resume," said Johnson, who won the 2016 US Open.

"We get paid very, very well if we win."