Updated - 9.30 p.m. Red Bull's Sebastian Vettel posted the fastest time in the first two practice sessions for the U.S. Grand Prix as drivers got their first taste of Formula One's newest venue today.
Vettel, who can clinch a third straight drivers' title on Sunday at the $400 million Circuit of the Americas, clocked a best lap of one minute 38.125 seconds in the first session. He posted a time of 1m37.718s in the second.
McLaren's Lewis Hamilton, who won the last Formula One race held in the United States five years ago at Indianapolis, was second fastest in 1:39.543 in the first session bet Vettel's Red Bull team-mate Mark Webber came second in the second session, followed by Ferrari's Fernando Alonso and the McLarens of Hamilton and Jenson Button.
Ferrari's Fernando Alonso is 10 points behind championship leader Vettel and the only driver who can deny his German rival the title.
"The first reactions from the drivers are very positive," Red Bull's team principal Christian Horner told reporters. "It's been a positive start for us. We need to build on that momentum."
Vettel, 25, will be starting his 100th grand prix this weekend with Red Bull also poised to clinch the constructors' crown for the third year in a row.
Despite being a new circuit and the pressure of have a championship on the line, Horner said his team is trying to approach the U.S. Grand the same way it does every other race.
"The team's very focused," said Horner. "We're really concentrated on getting the most out of this weekend and trying not to allow other distractions to interfere with our preparation and performance.
"We've come here to do a job and then the championships will tend to take care of themselves.
"Our approach here is no different here to any other race. There's obviously a bit more hanging on it than others as we've got to the business end of the championship."
SECOND FREE PRACTICE TIMES
1. Sebastian Vettel (Germany) RedBull - Renault 1:37.718 2. Mark Webber (Australia) RedBull - Renault 1:38.475 3. Fernando Alonso (Spain) Ferrari 1:38.483 4. Lewis Hamilton (Britain) McLaren 1:38.748 5. Jenson Button (Britain) McLaren 1:38.786 6. Felipe Massa (Brazil) Ferrari 1:39.029 7. Nico Rosberg (Germany) Mercedes 1:39.448 8. Bruno Senna (Brazil) Williams - Renault 1:39.531 9. Kamui Kobayashi (Japan) Sauber - Ferrari 1:39.653 10. Michael Schumacher (Germany) Mercedes 1:40.115 11. Kimi Raikkonen (Finland) Lotus - Renault 1:40.166 12. Pastor Maldonado (Venezuela) Williams - Renault 1:40.230 13. Romain Grosjean (France) Lotus - Renault 1:40.286 14. Sergio Perez (Mexico) Sauber - Ferrari 1:40.326 15. Daniel Ricciardo (Australia) Toro Rosso - Ferrari 1:40.435 16. Jean-Eric Vergne (France) Toro Rosso - Ferrari 1:40.516 17. Nico Huelkenberg (Germany) Force India - Mercedes 1:40.700 18. Paul Di Resta (Britain) Force India - Mercedes 1:41.430 19. Heikki Kovalainen (Finland) Caterham - Renault 1:42.476 20. Timo Glock (Germany) Marussia - Cosworth 1:42.652 21. Vitaly Petrov (Russia) Caterham - Renault 1:42.846 22. Charles Pic (France) Marussia - Cosworth 1:43.538 23. Pedro de la Rosa (Spain) HRT - Cosworth 1:44.453 24. Narain Karthikeyan (India) HRT - Cosworth 1:45.114