Lewis Hamilton fastest in Brazilian Grand Prix practice
Mercedes driver Lewis Hamilton got his critical Brazilian Grand Prix weekend off to the ideal start with fastest time in first practice.
To take the title fight to the final race, Hamilton must stop team-mate Nico Rosberg winning the race on Sunday.
Hamilton was 0.230 seconds quicker than the German, who was only third, the two separated by Red Bull's Max Verstappen.
Hamilton was 0.096secs quicker than the Dutchman, whose team-mate Daniel Ricciardo was fourth fastest.
Hamilton was faster on both the medium tyres that the Mercedes drivers ran early in the session - by 0.05secs - and on the softs later on.
Second practice is live on the Sport website and 5 live sports extra 16:00 GMT.
The session was held in hot and sunny conditions in Sao Paulo, but rain is expected later in the day and the weekend is forecasted to be cool and showery.
Wet conditions are likely to bring Red Bull into the mix for victory, which could play into Hamilton's hands.
McLaren driver Jenson Button, Hamilton's former team-mate, said: "If it's wet, it mixes things up. Lewis knows he's really good in the wet and can make a big points score. Nico knows there's a lot more to lose. I'm sure Nico wants it to be dry. But everyone watching wants it to be wet."
Rosberg has a 19-point advantage over Hamilton, who has won the last two races in the USA and Mexico.
A victory would extend Rosberg's advantage to at least 26 points, which means Hamilton could not overtake him in Abu Dhabi in two weeks' time.
Ricciardo said Mercedes were likely to finish one-two if the race is dry and if Rosberg is second behind Hamilton, then he would need only a third place in Abu Dhabi in two weeks' time to secure his first world title.
Rosberg says he is focusing only on trying to win in Brazil.
"It's awesome to be fighting for the world championship with two races to go and so, yeah, excited about the weekend, looking forward to it and of course going to try to go for the win," he said.
Behind the Mercedes and Red Bulls, Williams driver Valtteri Bottas was fifth fastest, split from team-mate Felipe Massa - in his last Brazilian Grand Prix - by the Force Indias of Sergio Perez and Nico Hulkenberg.
Ferrari drivers Sebastian Vettel and Kimi Raikkonen were only ninth and 10th, Vettel 1.672secs behind Hamilton and 0.002secs quicker than the Finn, but did not run on the soft tyre.
Ferrari ran only the medium, which is in the region of 0.7secs slower than the soft tyre used by all ahead of them to set their best times.
Vettel had a spin late in the session at the fast downhill left-hander called Mergulho, the penultimate corner on the track.
Jenson Button, two races from the likely end of his F1 career, was 13th, one place and 0.044secs ahead of McLaren team-mate Fernando Alonso.
Jolyon Palmer, confirmed as staying at Renault next season, was 19th fastest, his team-mate Kevin Magnussen sitting out the session as Russian GP2 driver Sergey Sirotkin was given a chance, ending up slowest of all.