The Briton leads his Brawn teammate Rubens Barrichello by 15 points, meaning that if he moves another 5 points ahead of the Brazilian in Japan, the drivers' title can be his with two races to spare.
If the 29-year-old wins on Sunday, he will be champion if Barrichello finishes fourth or lower. Button can also finish second and be champion at Suzuka, if Barrichello is no higher than sixth.
If Button is third and Barrichello is eighth, the Briton can also clinch the title in Japan, and if Barrichello fails to score a single point, Button only needs to finish fourth.
Red Bull's Sebastian Vettel also still has an outside mathematical chance of the title, with the German a distant 25 points behind Button.
With three races to go, it means that if he wins in Japan with Button no higher than fifth, the championship battle will move on to the penultimate round at Interlagos.
If Vettel finishes second at Suzuka, Button only has to finish sixth to finish the German's championship chances, and if the 22-year-old is third, he will be out of the battle if Button scores a single point.
If Vettel finishes fourth at Suzuka, his championship challenge will automatically be over.
As for the constructors' championship, Brawn can secure it in Japan this weekend if only rivals Red Bull fail to the close the points gap by an unlikely 11 points.
Many observers believe Sunday at Singapore put both titles effectively in Brawn and Button's hands, but team boss Ross Brawn does not agree.
"Until it is done, it is not done," he is quoted as saying by the Evening Standard.