Sebastian Vettel admitted to not concentrating hard enough on Friday when he crashed in Suzuka practice.
If Friday's fastest driver Jenson Button wins on Sunday, and runaway championship leader Vettel crashes again, the title fight will move on to Korea.
On the other hand, Red Bull's Vettel - the back-to-back Japanese Grand Prix winner - needs only to finish tenth to guarantee his second crown.
"I had a good reminder in practice not to start thinking about something else," he admitted on Friday.
"It was not really a big mistake, but maybe at that moment I was not 100 per cent awake, and mistakes around here can be quite costly."