Nico Rosberg made the most of the Mercedes F-duct to beat the McLarens to the fastest time in opening practice in Valencia.
The German had been contesting the top spot with Jenson Button and Lewis Hamilton for much of the morning on the dusty Spanish street track. With 15 minutes to go, Rosberg was asked to do a back-to-back test running a lap without activating the F-duct and then one with the system – which neatly demonstrated the device's effectiveness as he jumped to first with a 1m41.175sec lap using the F-duct.
Hamilton remained second for McLaren, 0.164sec down on Rosberg and 0.044sec ahead of his teammate Button.
Robert Kubica put Renault fourth, half a second off the pace, with fifth-placed Felipe Massa (Ferrari) a second down on Rosberg but just fractionally faster than the Red Bulls, Michael Schumacher's Mercedes, Fernando Alonso in the second Ferrari, and Williams' Rubens Barrichello.
Ferrari spent the session evaluating its new exhaust system, with Alonso carrying out a heat soak test in the pit lane exit and his car running with temperature-sensitive stickers.
Tire graining was an issue, and many drivers visited the run-off areas, but no one got as far as the barriers. There was a brief red flag early on, though, when Bruno Senna's Hispania shed a mirror. The detached part was run over and smashed by Sebastien Buemi's Toro Rosso, prompting a brief stoppage to sweep the debris away.
Hispania's mileage was later limited as driveshaft and gearbox problems kept both Senna and test driver Christian Klien – replacing Karun Chandhok this morning – in the pits. Klien was one of two test drivers in action, with Paul di Resta out in Adrian Sutil's Force India. The Scot took 16th, two places and one tenth of a second behind teammate Tonio Liuzzi.
Pos Driver Team Time Laps
1. Rosberg Mercedes 1:41.175 16
2. Hamilton McLaren-Mercedes 1:41.339 + 0.164 19
3. Button McLaren-Mercedes 1:41.383 + 0.208 21
4. Kubica Renault 1:41.715 + 0.540 20
5. Massa Ferrari 1:42.182 + 1.007 21
6. Vettel Red Bull-Renault 1:42.216 + 1.041 24
7. Webber Red Bull-Renault 1:42.275 + 1.100 17
8. Schumacher Mercedes 1:42.312 + 1.137 18
9. Alonso Ferrari 1:42.421 + 1.246 22
10. Barrichello Williams-Cosworth 1:42.463 + 1.288 21
11. Hulkenberg Williams-Cosworth 1:42.707 + 1.532 23
12. Petrov Renault 1:42.962 + 1.787 17
13. Buemi Toro Rosso-Ferrari 1:43.310 + 2.135 23
14. Liuzzi Force India-Mercedes 1:43.380 + 2.205 19
15. de la Rosa Sauber-Ferrari 1:43.397 + 2.222 21
16. di Resta Force India-Mercedes 1:43.437 + 2.262 18
17. Kobayashi Sauber-Ferrari 1:43.729 + 2.554 21
18. Alguersuari Toro Rosso-Ferrari 1:44.183 + 3.008 21
19. Kovalainen Lotus-Cosworth 1:44.491 + 3.316 21
20. Glock Virgin-Cosworth 1:45.653 + 4.478 23
21. Senna HRT-Cosworth 1:47.123 + 5.948 17
22. Trulli Lotus-Cosworth 1:47.285 + 6.110 18
23. Klien HRT-Cosworth 1:47.343 + 6.168 14
24. di Grassi Virgin-Cosworth 1:47.356 + 6.181 24
All Timing Unofficial