F1: Formula One championship leader Sebastian Vettel lapped fastest on Friday in opening practice for an Indian Grand Prix that could bring him a fourth win in a row on Sunday.
Red Bull's 25-year-old German, who leads Ferrari's Fernando Alonso by six points with four races remaining, set a best time of one minute 27.619 seconds at the hazy Buddh International Circuit south of New Delhi.
McLaren's Jenson Button was second fastest, 0.310 slower, with Alonso third.
The top three in first practice were in the same order as last year's podium finishers at the inaugural Indian Grand Prix, which Vettel won having already clinched his second title.
McLaren's Lewis Hamilton was fourth on the timesheets with Australian Mark Webber fifth.
Kimi Raikkonen, third in the championship with Lotus, was 10th fastest on his first experience of the track. Last year's race took place before he began his comeback after a two-season absence.
Mexican Esteban Gutierrez replaced compatriot Sergio Perez at Sauber, after the regular race driver was reportedly unwell, and was 20th.
Perez, who is likely to return for second practice and the rest of the weekend, appeared to disagree about his health and said on Twitter he was ready to drive and it had been a team decision.
Gutierrez is widely expected to replace Perez next season, with the older Mexican moving to McLaren to take over from Hamilton when he goes to Mercedes.
With the little-used track dusty at the outset, teams took their time to progress beyond installation laps and then focused on gathering data and testing updates before tyre work in the afternoon.
Ferrari, whose wind tunnel data has let them down this season, tried out updated rear and front wings they hope will help Alonso take the fight to Vettel.