Red Bull's Sebastian Vettel headed McLaren's Jenson Button and Ferrari's Fernando Alonso in first practice at the Indian Grand Prix.
The German, who took the world championship lead with victory in the last race in Korea ended up 0.310 seconds clear of Button.
Alonso was 0.435 seconds behind his main title rival, with McLaren's Lewis Hamilton 0.002secs behind the Ferrari.
Red Bull's Mark Webber was fifth ahead of Mercedes driver Nico Rosberg.
Ferrari's Felipe Massa was seventh, ahead of Mercedes driver Michael Schumacher, Toro Rosso's Daniel Ricciardo and Lotus's Kimi Raikkonen 10th.
Mexican Esteban Gutierrez, standing in during the first session for regular driver Sergio Perez, was 20th fastest, 1.4secs slower than his team-mate Kamui Kobayashi.
He had one near-miss when he lost the car through the fast chicane at Turns Eight and Nine but managed to recover it before hitting the wall.
Sauber said Gutierrez drove because Perez was "unwell", but Perez said on his Twitter account that while he had a cold on Thursday he was feeling well on Friday morning.
The teams seem closely matched - although Vettel's time of one minute 27.619 seconds was faster by a significant amount with a lap he produced right at the end of the session, Hamilton aborted a lap earlier on that looked as if it would have been a similar time.
Alonso and Ferrari spent the session comparing different designs of front and rear wing as they attempt to claw back some of the advantage Red Bull have created with developments introduced over the last three races, all of which Vettel has won.
BBC F1 technical analyst Gary Anderson said: "This race will be won on pure speed. I don't think there will be much tactics or strategy involved, so all the teams will be concentrating on ensuring the cars are as fast as possible in qualifying trim. It will be important to be a the front of the grid."
The track was very dusty at the start of the session and the teams took some time before they started to do any extensive running.
But although a few drivers ran wide, there were no major incidents.