Double world champion Fernando Alonso was fastest in both free practice sessions for the US Grand Prix on Friday, with McLaren team mate Lewis Hamilton a close second in the afternoon.
The Spaniard, who trails Hamilton by eight points in the championship standings after six races, underlined his determination to get back to the top on a sizzling day at the Indianapolis Motor Speedway.
He was fastest in the morning with a lap of one minute 11.925 seconds and quickest again in the afternoon with a time of 1:12.156.
Hamilton, whose only experience of the track is from video games, quickly got to grips with the 2.6 mile (4.1km) layout and ended the second session just 0.153 seconds slower.
The 22-year-old Briton, who in Canada last Sunday became the first black driver to win a Formula One race, had several brushes with the walls on his way to setting the third best time in the morning.
After struggling in the last two races, Ferrari were close behind McLaren with Brazilian Felipe Massa clocking the third quickest time in the second session ahead of Finnish team mate Kimi Raikkonen.
Indianapolis has provided a happy hunting ground for Ferrari, having won six of seven grands prix staged there since 2000, and the Italian team are looking to come back strongly and cut McLaren's 28 point lead in the constructors' standings.
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 in the morning but only 11th in the afternoon.
