"Obviously, both cars have got bits that they (the engineers) are having a look at for future events", said Horner.
Hamilton, who has a fourth star on his crash helmet this weekend to represent his latest world title triumph, arrived here in Sao Paulo in the spotlight following claims that he had avoided a £3.3million Value-Added Tax charge on his private jet. "It was pretty exciting to come to the track with the cars being so much faster this year". Williams' Felipe Massa, set for his final Brazilian Grand Prix before retiring from F1 for good, was eighth - an encouraging start for the team on a weekend it could secure fifth in what has been a nervy midfield battle.
Romain Grosjean spun during the session on route to 14th, ahead of Toro Rosso pair Pierre Gasly and Brendon Hartley, who are both set for hefty engine penalties this weekend after failures in FP1.
"Unfortunately the tyres don't last very long so you only get one or two laps on the short runs".
"Nothing has changed", Hamilton said, when asked if he would treat the rest of the season differently. "I think we can fine-tune the balance and that should help us", Vettel said.
Vikings activate Bridgewater, put Bradford on IR
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Hamilton, who accused Renault's Nico Hulkenberg over the radio of risky driving in forcing him wide onto the runoff in the morning, was half a second faster than Ferrari's Kimi Raikkonen before lunch.
Lewis Hamilton may have won the Drivers' Championship, but he isn't out of the spotlight just yet. Red Bull and Ferrari alternated the next four positions, with Daniel Ricciardo finishing third quickest behind the Mercedes drivers and ahead of Sebastian Vettel, teammate Max Verstappen and Kimi Raikkonen.
"As I said before, my mentality for the last two races is to win - and I have not been told otherwise".
"There are still two races to go".
British driver George Russell, the 19-year-old GP3 champion, made his grand prix weekend debut with Force India and was an impressive 12th fastest at an unfamiliar circuit and in a auto he had not driven before.