Button says it is unlikely he will win the title in Japan on Sunday
World championship leader Jenson Button has admitted he is finding it "tough" to deal with the pressure of battling for the Formula 1 drivers' title.
The Englishman can win the championship in Japan on Sunday if he scores five more points than his closest rival, his Brawn team-mate Rubens Barrichello.
"It's tough, but it's also very exciting and I would not change it for the world," Button said.
"I don't come into the race thinking I am going to seal the title here."
Button is 15 points ahead of Barrichello and a further 10 in front of Red Bull's Sebastian Vettel, the only other man with a chance of becoming champion.
Because Button's tally of six wins cannot be matched by either Barrichello or Vettel in the remaining three races, the 29-year-old will be champion if by the end of Sunday's race he has at least 20 more points than his rivals.
F1 WORLD CHAMPIONSHIP MATHS
Button will win the title in Japan if...
He wins and Barrichello is lower than third
He is second and Barrichello is lower than fifth
He is third and Barrichello is lower than seventh
If he is fourth and Barrichello is lower than eighth
Button described the pressure inherent in going for the championship as "part of the challenge".
And he said he thought taking five more points than Barrichello would be difficult because the Brazilian has been in such strong form.
Button has not win since the Turkish Grand Prix in June, whereas Barrichello has won two of the last four races and has outscored him in the last seven races, scoring 34 points to Button's 23.
"To beat your team-mate by five points when he's at his prime, as he is at the moment, is very difficult," Button said.
"There are so many things that can happen this weekend. There are three people in the running for the title and I am one of them.
"The most important thing for me to do is to work as hard as I can on Friday and Saturday to get the car right for qualifying and the race.
"I shouldn't be thinking about anything else. When I'm away from the circuit I spend time with my friends and they know better than to ask me about the championship."
He added: "As kids we all want to race in F1 and be world champion, but we don't often say 'I want to win it by this time or by this much'.
"My dream is not to win it in Suzuka, my dream is just to win it."
Barrichello, who has been told the team will not favour either driver, said: "I am really relaxed. I have a good chance, the best chance in a long time.
"I just have to be cool and win the race and forget about the rest.
"The team is handling that quite well. It will be very hard to get a different strategy unless I'm outside the top 10 - which I don't want to be."
Barrichello said that Brawn expected Red Bull to be the team to beat in Japan.
"We always knew that coming to Suzuka it was always a track that very much favoured the Red Bulls, so we have that in mind.
"It has been a little bit more humid than normal for Suzuka. So if it's a little bit hotter, that will help our tyre situation. Having said that, I love the track, and I will give my very best."
After two years at Fuji, the Japanese GP is returning to Suzuka's formidable figure-of-eight circuit for the first time since 2006.
Button is relishing a return to the circuit, which is owned by Honda - ironically the team from which Brawn emerged after the Japanese car giant pulled out of F1 last December.
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