Stenson holds a commanding lead of 252,163 points over the second-placed Englishman and will secure a second order of merit title in four years if he wins in South Africa and Willett is outside the leading 10 players.
Any other result and the race to end the season on top of the pile will continue at the $8 million DP World Tour Championship in Dubai next week.
Stenson missed last week's Turkish Airlines Open and the out-of-form Willett spurned the chance to close the gap by finishing in a tie for 68th place.
“I've had a really good year and it would be nice to finish off by being Europe's number one,” Stenson told a news conference at the Gary Player Country Club on Tuesday.
“I'm sure Danny's going to try and find some game over the last couple of weeks and push me to the limit.”
Third-placed Rory McIlroy, who has opted not to play this week, will hope his money-list ambitions are still intact when he returns in Dubai.
Stenson, though, would cap a dream year if he ended up as Europe's number one.
“It was kind of the final piece of the puzzle,” he said in reference to his Open win at Troon in July.
“It's still so fresh that you get reminded about it so much but you want to move on and focus on what's on in the future.”
The Nedbank event starts on Thursday.
Original source: Stenson expecting Willett to push him at Sun City