|Track temperatures were much higher for the start of second practice [EPA]
Ferrari's Fernando Alonso splashed his way to the top of the timing screens in a rain-soaked free practice for the Belgian Grand Prix.
The double world champion, chasing his team's fourth successive Spa success, was quickest in the morning and afternoon sessions at the longest track on the calendar.
The Spaniard set the best time of the day, a lap of one minute 49.032 seconds, at the end of an interrupted second session on a drying track after heavy cloudbursts on Friday morning.
The session was halted for 12 of the last 15 minutes, frustratingly just as there was the chance of some dry running, after reports that spectators had strayed into dangerous positions around the circuit.
Alonso's late lap ousted Force India's Adrian Sutil from the top at a track where the German's team took their first pole position, podium and points last year with Italian Giancarlo Fisichella.
McLaren's Lewis Hamilton was second and third fastest respectively with Robert Kubica making good use of the new 'F-duct' on his Renault to lay down the third and fourth best times.
Red Bull's championship leader Mark Webber, presented before the session with a cake topped with a chocolate racing car on his 34th birthday, was only seventh in the morning, with German team mate Sebastian Vettel fourth.
The Australian, four points clear of Hamilton at the top of the standings with seven races remaining, fell to 18th after lunch.
McLaren's world champion, Jenson Button, fourth in the championship with 14 points to make up on Webber, was sixth and seventh fastest in the two sessions.
Belgian Grand Prix second free practice times from Spa-Francorchamps.
1. Fernando Alonso (Spain) Ferrari 1:49.032
2. Adrian Sutil (Germany) Force India-Mercedes 1:49.157
3. Lewis Hamilton (Britain) McLaren 1:49.248
4. Robert Kubica (Poland) Renault 1:49.282
5. Felipe Massa (Brazil) Ferrari 1:49.588
6. Sebastian Vettel (Germany) RedBull-Renault 1:49.689
7. Jenson Button (Britain) McLaren 1:49.755
8. Pedro de la Rosa (Spain) BMW Sauber-Ferrari 1:50.081
9. Rubens Barrichello (Brazil) Williams-Cosworth 1:50.128
10. Kamui Kobayashi (Japan) BMW Sauber-Ferrari 1:50.200
11. Vitaly Petrov (Russia) Renault 1:50.251
12. Michael Schumacher (Germany) Mercedes 1:50.341
13. Nico Rosberg (Germany) Mercedes 1:50.382
14. Jaime Alguersuari (Spain) Toro Rosso-Ferrari 1:50.682
15. Nico Huelkenberg (Germany) Williams-Cosworth 1:50.831
16. Vitantonio Liuzzi (Italy) Force India-Mercedes 1:51.520
17. Sebastien Buemi (Switzerland) Toro Rosso-Ferrari 1:51.523
18. Mark Webber (Australia) RedBull-Renault 1:51.636
19. Heikki Kovalainen (Finland) Lotus-Cosworth 1:53.480
20. Jarno Trulli (Italy) Lotus-Cosworth 1:53.639
21. Lucas Di Grassi (Brazil) Virgin-Cosworth 1:54.325
22. Bruno Senna (Brazil) HRT-Cosworth 1:55.751
23. Sakon Yamamoto (Japan) HRT-Cosworth 1:56.039
24. Timo Glock (Germany) Virgin-Cosworth 2:03.179