The American won by two shots at the Deutsche Bank Championship on Sunday to surge to the top of the leaderboard, but a host of players can overhaul the 29-year-old with a strong showing at Cherry Hills in the penultimate play-off event.
World number one Rory McIlroy, winner of two majors this year, sits second after a fifth-place finish in Boston, but there are some big names who are facing a battle to climb into the top 30 - a prerequisite to qualify for the finale.
Last year's FedEx Cup champion Henrik Stenson is down in 55th and will realistically need a top-three berth to continue his title defence.
The field will be a man short, too, with Dustin Johnson on a leave of absence, leaving 69 competitors to take the course in Colorado on Thursday.
Those residing just inside the top 30 can ill afford to relax, with a huge group of rivals ready to seize on an opportunity to displace them.
The picture can change drastically and that was demonstrated very clearly by Geoff Ogilvy at the Deutsche Bank Championship.
Ogilvy went into the event 100th on the ladder - the lowest-ranked player in the field - but tied for second to jump up to 24th.
Two players with plenty to play for received timely boosts when they were named as Tom Watson's captain's pick for this month's Ryder Cup.
Hunter Mahan and Keegan Bradley, as well as Webb Simpson, got the nod for the United States as they seek revenge for Europe's stunning triumph at Medinah in 2012.
But before their focus can turn to Gleneagles, both have personal honours to compete for, with Mahan - winner at The Barclays last month - sitting third in the FedEx Cup points table.
While his sights will be set firmly on overall glory, his compatriot occupies 28th spot and has little margin for error in his bid to claim a place at the Tour Championship in Atlanta later this month.