AUSTIN, Texas, Nov 16 - Red Bull's Sebastian Vettel posted the fastest time in the first practice session for the 2012 US Grand Prix as drivers got their first taste of F1 newest venue.Vettel, who can clinch a third straight drivers' title on November 2012 at the Circuit of the Americas, clocked a best lap of 1min38.125 around the 5.516km track.McLaren's Lewis Hamilton, who won the last Formula 1 race held in the United States five years ago at Indianapolis, was second fastest in 1min39.543 although times had little significance in a session that was more about familiarisation.STARS AND STRIPES RETURNFerrari's Fernando Alonso, 10 points behind championship leader Vettel and the only driver who can deny his rival the title, had the third best time in 1min40.337.Red Bull's team principal Christian Horner said: "The first reactions from the drivers are very positive. 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.The morning session, run in front of mostly empty grandstands, produced a few thrills as drivers came to grips on the slick undulating circuit.While the 90-minute practice finished without major incident there were plenty of spins and more than a few forays into runoff areas as drivers tested the limits of the track.Horner said: "The circuit was very dirty this morning as you would expect with a new surface, so it took a while and you could see the evolution of the track was getting quicker and quicker every lap. "It's pretty cool here, I think probably cooler than all of us thought. So it's taken a few laps for the tires to cool up to temperature."But I think that as the rubber goes down and the drivers push harder, then that lap time will come much sooner."Drivers will be back out on the track later for another 90 minute free practise where times will continue to drop.Despite being a new circuit and the pressure of have a championship on the line, Horner said his team is trying to approach the US Grand the same way it does every other race.Horner said: "The team's very focused. 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."2012 United States Grand Prix - First practice session times 1 Sebastian Vettel (Germany) Red Bull 1min38.125 2 Lewis Hamilton (Britain) McLaren 1min39.543 3 Fernando Alonso (Spain) Ferrari 1min40.337 4 Jenson Button (Britain) McLaren 1min40.528 5 Mark Webber (Australia) Red Bull 1min40.650 6 Felipe Massa (Brazil) Ferrari 1min40.966 7 Nico Huelkenberg (Germany) Force India 1min41.023 8 Kamui Kobayashi (Japan) Sauber - Ferrari 1min41.036 9 Nico Rosberg (Germany) Mercedes 1min41.159 10 Sergio Perez (Mexico) Sauber - Ferrari 1min41.473 11 Paul Di Resta (Britain) Force India 1min41.783 12 Daniel Ricciardo (Australia) Toro Rosso 1min41.825 13 Jean-Eric Vergne (France) Toro Rosso 1min41.833 14 Kimi Raikkonen (Finland) Lotus 1min41.880 15 Romain Grosjean (France) Lotus 1min41.998 16 Pastor Maldonado (Venezuela) Williams 1min42.539 17 Michael Schumacher (Germany) Mercedes 1min42.588 18 Charles Pic (France) Marussia 1min43.288 19 Heikki Kovalainen (Finland) Caterham 1min43.443 20 Vitaly Petrov (Russia) Caterham 1min43.522 21 Timo Glock (Germany) Marussia 1min44.464 22 Bruno Senna (Brazil) Williams 1min44.548 23 Pedro de la Rosa (Spain) HRT 1min46.917 24 Ma Qinghua (China) HRT 1min48.559Stay with Wheels24 for the US Grand Prix weekend.