By Andrew Benson
BBC Sport in Sao Paulo
Red Bull drivers Sebastian Vettel and Mark Webber emphasised they are still title contenders by dominating first practice for the Brazilian Grand Prix.
Vettel - who is 25 points behind the championship leader, Ferrari's Fernando Alonso - set the fastest time, 0.482 seconds quicker than Webber.
Australian Webber, 11 points behind Alonso, was just 0.035secs ahead of McLaren's Lewis Hamilton.
Hamilton's team-mate Jenson Button was fourth, with Alonso only 13th.
The Spaniard's car stopped out on the track towards the end of the session. Ferrari said the engine in the car was at the end of its life and the failure happened two laps earlier than expected.
The team had anyway been planning to change Alonso's engine between first and second practice, which starts at 1600 GMT.
Vettel's lap of one minute 12.328 seconds may appear ominous for the rest, but is not necessarily an accurate indication of form for qualifying and the race.
The teams spent the sessions evaluating set-up and various new parts on their cars.
As is normal, the top drivers waited in their garages for more than half the session so as not to waste their tyres on a dirty track and to limit mileage on their engines.
FIVE-WAY TITLE BATTLE EXPLAINED
1 ALONSO 231pts
2 WEBBER 220pts
3 HAMILTON 210pts
4 VETTEL 206pts
5 BUTTON 189pts
If Alonso wins in Brazil, he will be champion unless Webber is higher than fourth
If Alonso is second, he will be champion unless Webber is higher than eighth, Hamilton higher than fourth or Vettel wins
If Alonso is third, he will be champion unless Webber finishes in the top 10, Hamilton in the top four and Vettel in the top three
If Alonso does not finish on the podium, it will go to Abu Dhabi
Button can only stay in contention if he finishes first or second but is out if Alonso finishes in the top six or if Webber is in the top two
Vettel must beat Alonso on track to stay in contention
Renault's Robert Kubica was the first serious contender to show his hand, setting a lap of one minute 13.462 seconds after 50 minutes of the 90-minute session.
But the Pole soon lost top spot when the title contenders emerged on to the track.
Webber was the first to beat Kubica, with a 1:13.168, before Hamilton dipped underneath that with a 1:13.138.
Vettel then dipped below the 73-second barrier with a 1:12.946, Hamilton beat that with a 1:12.845 before the German knocked half a second off that with a 1:12.351.
Kubica ended up fifth, ahead of Mercedes driver Nico Rosberg, whose team-mate Michael Schumacher was eighth behind the Williams driver Rubens Barrichello.
Force India's Adrian Sutil was ninth, ahead of the Sauber of Nick Heidfeld.
Renault's Vitaly Petrov suffered a crash when he lost control going into Turn Seven, a quick uphill right-hander known as Ferra Dura.
Heidfeld's team-mate Kamui Kobayashi also crashed at Ferra Dura, a couple of minutes after Petrov and just before the end of the session.
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