Lewis Hamilton was fastest by nearly a second in the opening free practice session in Turkey, leading his team-mate Jenson Button in a McLaren one-two.
Hamilton moved to the front at the end of the short but frenetic period of mid-session place-changing that followed a very quiet start to the morning.
Although several teams - including Mercedes and Force India in particular - conducted more installation runs than usual as they tested new parts, it was half an hour before anyone tried a flying lap, and a further 15 minutes before the big-hitters got up to speed.
When they did so, Sebastian Vettel (Red Bull) and Robert Kubica (Renault) took turns in first place before the McLaren team-mates started a private battle. Hamilton went quickest with a 1m29.672s, but was then pipped by Button's 1m29.623s.
Five minutes later though Hamilton produced a 1m28.653s to go fastest by 0.962 seconds, which is how things remained for the rest of the morning.
Mercedes took third and fourth, with Michael Schumacher just over 0.1s up on Nico Rosberg. Vettel and Kubica completed the top six, ahead of Vitaly Petrov in a strong seventh in the second Renault. Championship leader Mark Webber was eighth for Red Bull, while Fernando Alonso was Ferrari's top runner in ninth.
While many people explored the run-off areas, especially Turn 1, 10th-placed Adrian Sutil had the only accident of the session. He lost control of his Force India at the daunting Turn 8 with two minutes to go and spun backwards into the barriers, causing substantial damage to the car.
Lotus's Heikki Kovalainen was the best among the group of new teams, and was within half a second of Toro Rosso driver Jaime Alguersuari's pace.
Bruno Senna handed his Hispania to test driver Sakon Yamamoto for the morning, with the former Super Aguri and Spyker man slowest of all as he settled in.
His team-mate Karun Chandhok lost a lot of time with a throttle problem that left him crawling back to the pits at little more than walking pace, but he made it to the garage and rejoined after repairs.
Pos Driver Team Time Laps 1. Hamilton McLaren-Mercedes 1:28.653 20 2. Button McLaren-Mercedes 1:29.615 + 0.962 20 3. Schumacher Mercedes 1:29.750 + 1.097 24 4. Rosberg Mercedes 1:29.855 + 1.202 24 5. Vettel Red Bull-Renault 1:29.867 + 1.214 30 6. Kubica Renault 1:30.061 + 1.408 23 7. Petrov Renault 1:30.065 + 1.412 24 8. Webber Red Bull-Renault 1:30.097 + 1.444 26 9. Alonso Ferrari 1:30.294 + 1.641 20 10. Sutil Force India-Mercedes 1:30.501 + 1.848 17 11. Kobayashi Sauber-Ferrari 1:30.615 + 1.962 20 12. Liuzzi Force India-Mercedes 1:30.853 + 2.200 21 13. Massa Ferrari 1:30.867 + 2.214 21 14. Buemi Toro Rosso-Ferrari 1:31.011 + 2.358 23 15. de la Rosa Sauber-Ferrari 1:31.238 + 2.585 17 16. Hulkenberg Williams-Cosworth 1:31.355 + 2.702 23 17. Barrichello Williams-Cosworth 1:31.464 + 2.811 19 18. Alguersuari Toro Rosso-Ferrari 1:31.735 + 3.082 27 19. Kovalainen Lotus-Cosworth 1:32.161 + 3.508 24 20. Trulli Lotus-Cosworth 1:32.990 + 4.337 22 21. Chandhok HRT-Cosworth 1:34.876 + 6.223 13 22. di Grassi Virgin-Cosworth 1:35.137 + 6.484 21 23. Glock Virgin-Cosworth 1:35.583 + 6.930 15 24. Yamamoto HRT-Cosworth 1:36.137 + 7.484 26 All Timing Unofficial