Lewis Hamilton topped opening practice ahead of the United States Grand Prix for Mercedes.
Hamilton edged his team-mate Rosberg to the top spot at the Circuit of the Americas with a lap of 1:39.941, two tenths of a second clear of his title rival, while Jenson Button, who topped the timesheets for the first hour of the session, was third for McLaren, a tenth down on Rosberg.
Daniil Kvyat, who debuted in practice at Austin last year, was fourth for Toro Rosso, a tenth up on Kevin Magnussen in the second McLaren.
Fernando Alonso experimented with two front wings on his way to sixth for Ferrari, over a second down on Hamilton’s session topping time, but ahead of Sebastian Vettel, who is expected to start Sunday’s race from the pitlane after a change of power unit.
Felipe Nasr, standing in for Valtteri Bottas at Williams in the opening session, was eighth, ahead of Force India’s Nico Hulkeneberg, while Max Verstappen – running in FP1 in place of Jean-Eric Vergne – rounded out the top ten, nine tenths down on Kvyat in the sister Toro Rosso.
Kimi Raikkonen ended practice just 12th, a fraction behind Felipe Massa, after a bizarre incident in the closing minutes of the session saw him grind to a halt in the pitlane after he missed his garage while attempting to avoid a slow Romain Grosjean.
Pastor Maldonado was 13th for Lotus after a spin at Turn 6, while Adrian Sutil survived a similar off at Turn 19 to finish 14th, ahead of Sergio Perez and Esteban Gutierrez.
Daniel Ricciardo completed just five laps for Red Bull after an early ERS problem saw him confined to the garage, while Grosjean, who trialled a new Mercedes style nose for Lotus was 18th, the last of the runners.
The cars notably returned to the circuit at the end of the session to evaluate the FIA’s proposed virtual safety car system, a safety measure which has been prompted by Jules Bianchi’s accident during the Japanese Grand Prix.
Image courtesy of Daimler