Lewis Hamilton top in Brazilian Grand Prix second practice
Lewis Hamilton topped both Friday practice sessions at the start of a Brazilian Grand Prix weekend that is critical to his title hopes.
If Mercedes team-mate Nico Rosberg wins on Sunday, the German will become champion for the first time.
Hamilton was 0.03 seconds quicker than Rosberg over one flying lap and also had a clear advantage on longer runs.
The Mercedes duo's closest rivals at Interlagos were the Williams pair of Valtteri Bottas and Felipe Massa.
"There is more to come," said Hamilton. "In previous years, I always struggled with the rear end and this weekend that doesn't seem to be the problem.
"I hope that continues but also I prepared a little bit differently this weekend and it seems to be working."
Bottas was 0.39secs behind Hamilton and 0.028secs ahead of Brazilian Massa, who is racing in his home grand prix for the last time after announcing he will retire at the end of the season.
The unexpected performance of the Williams cars pushed the Red Bulls of Daniel Ricciardo and Max Verstappen down to fifth and sixth places respectively, half a second behind the Mercedes.
The Red Bulls are expected to closer to Hamilton and Rosberg in the race.
Final practice (13:00 GMT) and qualifying (16:00) take place on Saturday and are live on the BBC Sport website and radio 5 live sports extra.
- Hamilton v Rosberg: How the 2016 title may be decided
- Will Rosberg join the list of championship winners in Brazil?
Rain could spice things up
Friday practice was held in hot and sunny conditions but cooler weather is predicted for the weekend and rain is forecast for race day, which would allow Red Bull to challenge Mercedes.
In the dry, however, Mercedes are in a league of their own - as was Hamilton for much of the time on Friday.
The margin between him and Rosberg was close in the second session but the Briton was 0.23secs quicker in the first.
In the race-simulation runs on the soft tyre in the second half of the second session, Hamilton was, on average, just under 0.5secs quicker than Rosberg, whose advantage over the Red Bulls was 0.2secs.
The margin between Hamilton and Rosberg was much smaller in their later runs on the medium tyre but still about 0.2secs in the world champion's favour.
"It's been a good day," said Hamilton. "The car is feeling really good. It's pretty tough out here physically right now with the heat as high as it is.
"Finding the right balance isn't easy either in these conditions as the tyres are getting really hot. But our long run pace seems to be strong, so we can be happy with the start we've made."
Ferrari appear to be struggling, with Sebastian Vettel and Kimi Raikkonen seventh and eighth fastest overall.
They are lagging behind Mercedes and Red Bull on race pace as well.
Force India's Nico Hulkenberg was ninth quickest ahead of the McLarens of Jenson Button and Fernando Alonso.
The Spaniard provided some light relief when his car stopped on track because of a data anomaly in the water supply to the energy recovery system.
Alonso was stuck on the outside of Turn Three and, after watching the cars for a while, began playing football keepy-uppies with a stone after getting bored.
A cameraman then offered him a chair to sit in, reviving memories of his antics after breaking down in the same session last year in Brazil.
Last year, coming at the end of a season of reliability problems in an uncompetitive car, his mock sunbathing sparked an internet sensation and the hashtag 'Places Alonso would rather be'.
Alonso played up to the incident on Friday, briefly operating the camera he was sat behind and then waving to another camera.
Meanwhile, Raikkonen and Toro Rosso's Carlos Sainz have been called to see the stewards after an on-track incident during the session.
They were seen driving slowly alongside each other, perhaps because one felt the other had blocked him, before Raikkonen accelerated around the outside of Sainz and then cutting across him to enter the pits at the end of the lap.
According to article 27.5 of the sporting regulations: "At no time may a car be driven unnecessarily slowly, erratically or in a manner which could be deemed potentially dangerous to other drivers or any other person. This will apply whether any such car is being driven on the track, the pit entry or the pit lane."