Red Bull's Mark Webber hit the front as the Formula 1 field managed a few minutes of dry running in the second free practice session for the Belgian Grand Prix at Spa-Francorchamps.
Only the two Mercedes had been able to squeeze in flying laps on slicks in first practice before the rain arrived, and the track was damp again when the afternoon session got under way.
Conditions steadily improved, with the two Red Bulls, Fernando Alonso and Jenson Button all taking turns at the front before Webber set the 2m00.964s that would stand at the best intermediate tire lap of the session. Alonso then became the first to explore the circuit on slicks, and the Ferrari man immediately beat Webber's time by four seconds, before getting down to a 1m53s on the next lap.
Both Mercedes and both Red Bulls would have moments in first position during the frantic quarter of an hour that followed as everyone tried to make the most of what would prove to be the only dry segment of the session.
It was Webber who was on top on a 1m50.321s when the clouds opened once more with just under 40 minutes left, and although most drivers did eventually come back out to get some wet practice, there was no way anyone was going to improve their pace on what was soon a sodden circuit. Alonso ended up second, ahead of McLaren pair Jenson Button and Lewis Hamilton, and the second Ferrari of Felipe Massa.
Behind Nico Rosberg (Mercedes) and Sergio Perez (Sauber), Nico Hulkenberg was eighth in a rare Friday afternoon appearance for a reserve driver, Force India having hoped the morning would see the best of the weather. It was Adrian Sutil who stood aside for Hulkenberg, with Paul di Resta ninth in the repaired sister car, ahead of Vettel.
Morning pacesetter Michael Schumacher was 11th for Mercedes, while a steering problem left Renault's Vitaly Petrov at the back of the field.
Pos Driver Team/Car Time Gap Laps
1. Mark Webber Red Bull-Renault 1m50.321s 22
2. Fernando Alonso Ferrari 1m50.461s + 0.140s 18
3. Jenson Button McLaren-Mercedes 1m50.770s + 0.449s 9
4. Lewis Hamilton McLaren-Mercedes 1m50.838s + 0.517s 9
5. Felipe Massa Ferrari 1m51.218s + 0.897s 14
6. Nico Rosberg Mercedes 1m51.242s + 0.921s 22
7. Sergio Perez Sauber-Ferrari 1m51.655s + 1.334s 20
8. Nico Hulkenberg Force India-Mercedes 1m51.725s + 1.404s 17
9. Paul di Resta Force India-Mercedes 1m51.751s + 1.430s 8
10. Sebastian Vettel Red Bull-Renault 1m51.790s + 1.469s 13
11. Michael Schumacher Mercedes 1m51.922s + 1.601s 22
12. Pastor Maldonado Williams-Cosworth 1m52.750s + 2.429s 20
13. Kamui Kobayashi Sauber-Ferrari 1m52.780s + 2.459s 25
14. Jaime Alguersuari Toro Rosso-Ferrari 1m52.911s + 2.59 s 24
15. Sébastien Buemi Toro Rosso-Ferrari 1m53.009s + 2.688s 24
16. Rubens Barrichello Williams-Cosworth 1m53.156s + 2.835s 17
17. Bruno Senna Renault 1m53.835s + 3.514s 20
18. Jarno Trulli Lotus-Renault 1m55.051s + 4.730s 20
19. Timo Glock Virgin-Cosworth 1m55.494s + 5.173s 22
20. Heikki Kovalainen Lotus-Renault 1m56.202s + 5.881s 15
21. Jerome D'Ambrosio Virgin-Cosworth 1m56.816s + 6.495s 20
22. Tonio Liuzzi HRT-Cosworth 1m57.450s + 7.129s 19
23. Daniel Ricciardo HRT-Cosworth 1m57.612s + 7.291s 24
24. Vitaly Petrov Renault 2m02.234s + 11.913s 12
All timing unofficial