Vettel's Red Bull have reliability issues and Ferrari are worried about their qualifying performances.
Twice this season Vettel's chances have been wrecked by alternator failure – a fault which also ended Mark Webber's race in Texas on Sunday – and if the world champion fails to finish here on Sunday Alonso only has to claim a podium place to become an unlikely world champion.
"For sure, the alternator is a concern," the Red Bull team principal, Christian Horner, said. "It is the third failure we have had this year. It is something [engine supplier] Renault need to get on top of this week. They have run different solutions on different cars and hopefully they have enough data now to make sure we have a reliable version. It is not ideal at the moment.
"We have to approach this race as we have the previous 19. We have to go there, attack the weekend, and get the best out of ourselves, the car, the strategy, the drivers and reliability. Anything can happen, as we have seen this season. But it is good to be going there with a lead."
Ferrari have not been as quick as Red Bull or McLaren this season, but they have had the most reliable car, and Alonso's consistency means he is just 13 points behind Vettel going into the final round. Alonso, however, has not qualified in the top three since Germany in July, when he won pole and the race, and Ferrari know they have to improve their one-lap race to improve their chances at Interlagos.
"We always say it but we need to improve out qualifying pace," said the team principal, Stefano Domenicali. "Unfortunately, in Austin we had one of the worst qualifyings of our championship. So we need to make sure in Brazil it is a different situation and it doesn't happen again otherwise it will be very, very difficult."
Lewis Hamilton, the man who would be fighting for the title too but for McLaren's failings this year, is looking forward to the final tussle between Vettel and Alonso. "They are both fantastic drivers, and both have driven superbly all season," he said. "Now we'll see who takes the final honours – I hope it's an epic contest."
The teams have arrived in Brazil against a background of bloodshed. According to the city's public safety department, there have been 982 homicides here in the first nine months of the year, with reports of another 250 since then.
A department spokesman said the killing of police has been ordered by the imprisoned leaders of an organised crime gang called First Capital Command in reprisal for a crackdown on the drug trade. One team principal said last night: "We're taking no special precautions this year. We are not staying in gangland, though the track is near there. But we don't go out in team colours."
Two years ago armed men attempted to attack an armoured car carrying the defending world champion, Jenson Button. When asked about security this year Button said: "It's the same as last year. We are having armoured vehicles and a police escort. We had them last year after what happened the year before."
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