Fernando Alonso put Ferrari at the top of the times as first practice for the Belgian Grand Prix was significantly affected by a large dose of typical Spa weather.
Alonso's initial benchmark time of 2m01.223s, set halfway through the 90-minute session, allowed him to eclipse title rivals Lewis Hamilton (McLaren) and Sebastian Vettel (Red Bull).
Shortly after setting his time, Alonso then reported on the radio that the rain from Stavelot up to Blanchimont had become much worse, and pitted. Within minutes the track was saturated by an ocean of rain and everybody else followed suit.
Several drivers emerged from the pits in the last 10 minutes of the session, as the biblical weather instantly replaced itself with blue skies and puffy clouds, but the track was so saturated that improvements looked unlikely, as Felipe Massa proved by running wide at Pouhon.
But Alonso was having none of that and went faster still by lapping the majestic Belgian circuit in 2m00.797s fastest - as if just to make a point.
Hamilton did not go out again, but his lap was good enough to keep him second fastest.
The rain did not stop the F-duct equipped Robert Kubica from improving either as the Renault man jumped to third in the final minutes.
Vettel was fourth, ahead of Adrian Sutil, who is always good in these conditions. The German was fifth fastest for Force India having battled for the top spot early on with Toro Rosso's Jaime Alguersuari, who slipped down the order to 16th.
Jenson Button was not one of those drivers who went out, and thus dropped to sixth for McLaren. The world champion was followed by Hungaroring winner Mark Webber (Red Bull), Sauber's Kamui Kobayashi and Rubens Barrichello, who left it late to set a time for Williams. Mercedes' Micheal Schumacher completed the top 10.
Despite the weather, no one delivered their car back to the pits broken - though there were predictably several offs, notably for Schumacher, Heikki Kovalainen and Massa.
Pos Driver Car Time Gap Laps 1. Fernando Alonso Ferrari 2m00.797s 17 2. Lewis Hamilton McLaren-Mercedes 2m01.567s + 0.770s 7 3. Robert Kubica Renault 2m02.081s + 1.284s 14 4. Sebastian Vettel Red Bull-Renault 2m02.450s + 1.653s 11 5. Adrian Sutil Force India-Mercedes 2m02.646s + 1.849s 14 6. Jenson Button McLaren-Mercedes 2m02.913s + 2.116s 6 7. Mark Webber Red Bull-Renault 2m02.926s + 2.129s 11 8. Kamui Kobayashi BMW Sauber-Ferrari 2m03.401s + 2.604s 17 9. Rubens Barrichello Williams-Cosworth 2m03.424s + 2.627s 7 10. Michael Schumacher Mercedes 2m03.489s + 2.692s 9 11. Felipe Massa Ferrari 2m03.601s + 2.804s 17 12. Nico Hulkenberg Williams-Cosworth 2m03.649s + 2.852s 17 13. Nico Rosberg Mercedes 2m03.654s + 2.857s 6 14. Pedro de la Rosa BMW Sauber-Ferrari 2m03.851s + 3.054s 17 15. Vitantonio Liuzzi Force India-Mercedes 2m04.145s + 3.348s 12 16. Jaime Alguersuari Toro Rosso-Ferrari 2m04.250s + 3.453s 16 17. Vitaly Petrov Renault 2m04.690s + 3.893s 15 18. Sebastien Buemi Toro Rosso-Ferrari 2m05.680s + 4.883s 6 19. Timo Glock Virgin-Cosworth 2m05.697s + 4.900s 18 20. Lucas di Grassi Virgin-Cosworth 2m06.695s + 5.898s 14 21. Jarno Trulli Lotus-Cosworth 2m07.189s + 6.392s 15 22. Bruno Senna HRT-Cosworth 2m07.737s + 6.940s 13 23. Heikki Kovalainen Lotus-Cosworth 2m07.955s + 7.158s 15 24. Sakon Yamamoto HRT-Cosworth 2m10.507s + 9.710s 18 All timing unofficial