Willett had topped the money list since winning his first major title at the Masters in April, but was overtaken by Open champion Stenson at the end of October.
Stenson was joint second in the WGC-HSBC Champions in Shanghai as Willett could only finish 14 over par and 75th in the 78-man field at Sheshan International.
And Willett could not take advantage of Stenson’s absence from the Turkish Airlines Open last week, the 29-year-old finishing joint 68th to only reduce his deficit from 261,387 to 252,163 points.
With more than one million points on offer to the winner, a second win for 2008 champion Stenson at the Gary Player Country Club would give the Swede a second Race to Dubai title in four years if Willett finishes outside the top 10.
“I’ve had a really good year behind me and it would be nice to finish it off with being Europe’s number one,” Stenson said.
World number two Rory McIlroy will also be interested in the outcome as his slim hopes of a third successive Race to Dubai crown are out of his hands following his withdrawal from the Turkish Airlines Open due to security concerns. If Stenson is tied seventh with one other or better, or Willett is tied second with two others or better, McIlroy will not be able to win the title even if he defends his DP World Tour Championship title.
Meanwhile, Graeme McDowell admits he is disappointed to find himself in a near-identical position as he looks to defend his title in the OHL Classic at Mayakoba, Mexico.
McDowell went into last year’s event in Mexico without a top-10 finish since his opening event of the year and ranked 85th in the world, but went on to claim victory in a three-man play-off. However, the 37-year-old Irishman returns to Playa del Carmen just four places higher in the rankings than 12 months ago and in need of more good performances to book his place in next year’s Masters.
“It was a very important victory for me at the end of last season,” McDowell said.
“I’d dearly love to try and repeat it this week.
“I suppose I’m disappointed that I haven’t really kicked on in 2016 with that momentum but this year has been a funny one. When it’s been good, it’s been really good, when it’s been bad I’ve been going home on Friday nights.”
Former world number one Luke Donald, Ian Poulter and Waterford’s Seamus Power are also in the field.