Triple world champion Lewis Hamilton reminded Mercedes team mate Nico Rosberg that he will not hand over his Formula One title without a fight after dominating the first day of practice at the Brazilian Grand Prix.
The Briton, 19 points behind the German with two races remaining, was fastest in both sessions at a sunny Interlagos with his best lap of one minute 11.895 seconds set on soft compound tyres in the morning.
Rosberg was third, and 0.230 off the pace in that session, but ended the day second on the afternoon timesheets and just 0.030 slower.
Red Bull's Dutch teenager Max Verstappen was second in the morning but sixth after lunch, when the Williams pair of Valtteri Bottas and home favourite Felipe Massa were Mercedes' closest rivals.
Rosberg, who is unlikely to lose too much sleep over the Friday times, can clinch his first championship title if he wins on Sunday, wherever Hamilton finishes.
On paper he has a good chance, having won the last two Brazilian Grands Prix from pole position, but Hamilton - wearing an Ayrton Senna themed helmet this weekend - has the momentum after victories in Texas and Mexico.
The weather at Interlagos can change from sunshine to torrential rain in a matter of minutes and the race has a history of surprises and drama, meaning there is still everything to play for.
Australian Daniel Ricciardo was fourth and fifth fastest for Red Bull who have improved steadily this season and are the only team other than Mercedes to have won races.
Ferrari's Sebastian Vettel was ninth in the morning, on the slower medium tyres, after spinning off in the closing minutes - his comments over the radio swiftly bleeped out on the television feed.
The German, seventh in the second session, was warned after an expletive-laden outburst at the previous race in Mexico.
Russian reserve Sergey Sirotkin took Kevin Magnussen's place at Renault for the morning stint while Monegasque driver Charles Leclerc was given a practice run in Mexican Esteban Gutierrez's Haas.
McLaren's Fernando Alonso provided some laughs when his McLaren suffered an energy recovery problem and stopped trackside.
The Spaniard also broke down in practice at Interlagos last year, when he triggered a social media flurry by sitting on a marshal's folding chair and sunning himself with his feet resting on his helmet.
This time he again cast around for something to sit on, and found a television operator who offered him his place at the controls of the camera.