Double world champion Fernando Alonso set the fastest time for McLaren on Friday in the first free practice session for Sunday's US Grand Prix.
The Spaniard lapped the Indianapolis Motor Speedway in one minute 11.925 seconds, ahead of Germany's Nick Heidfeld in a BMW Sauber and McLaren teammate and championship leader Lewis Hamilton.
German teenager Sebastian Vettel, who will make his Formula One race debut on Sunday in place of injured Robert Kubica, was fourth quickest in a BMW Sauber followed by Ferrari's Kimi Raikkonen.
Alonso, who trails Hamilton by eight points in the championship standings, was the only driver to dip under 1:12.00 on a sizzling hot day at the Brickyard as he underlined his determination to get back on top.
Even more impressive was 19-year-old Vettel, the youngest driver on track, who turned consistently fast times throughout the morning.
Hamilton, who became the first black driver to win a Formula One race with his victory last Sunday at the Canadian Grand Prix, had several close brushes with the Brickyard's infamous walls but managed to steer clear of trouble.