Ferrari's Fernando Alonso set the pace as the skies cleared over Spa-Francorchamps and the Formula 1 field finally managed some dry running in Saturday morning practice.
Kimi Raikkonen put Lotus in second place, ahead of an impressive run from the Saubers of Sergio Perez and Kamui Kobayashi.
With no dry running on Friday, teams had to cram a lot of work into practice three. That meant a wild diversity of approach early on as some focused on heavy-fuel runs while others were clearly quickly into qualifying preparations.
That meant the unusual sight of the Marussias holding their own in the top five a long way into the session while the McLarens were towards the lower end of the top 20 initially.
Williams's Bruno Senna was the early pacesetter, before Ferrari hit the front. Alonso was onto soft tyres within 25 minutes, improving on his medium tyre benchmark of 1m50.936s to move further clear with a 1m50.690s.
That kept him in front for 10 minutes before Sauber showed great pace on softs, with Perez and Kobayashi holding a one-two for a spell.
They were briefly deposed by Romain Grosjean's Lotus - running medium tyres - and then Red Bull's Mark Webber, also on the harder rubber.
Sauber's speed was not a one-off as Perez and Kobayashi returned to the front going into the final five minutes, again using softs.
But the hard-charging Alonso fought back, catching some high-speed slides on the way to a 1m48.542s as the chequered flag neared.
That kept him on top, while Raikkonen slipped ahead of the Saubers for second, 0.141 seconds off the Ferrari.
McLaren's lead runner was Jenson Button in fifth position, seven spots ahead of Lewis Hamilton, as team appeared to stay focused on race preparation.
Felipe Massa looked capable of matching Ferrari team-mate Alonso's pace before losing time towards the end of his best lap, leaving him sixth.
The Red Bulls of Mark Webber and Sebastian Vettel were seventh and ninth, split by Romain Grosjean's Lotus, with Paul di Resta completing the top 10 for Force India.
While most drivers were able to make up for lost time in practice three, Nico Rosberg will go into qualifying with barely any dry running.
His Mercedes managed just five laps in the session before slowing to a halt at Pouhon with a mechanical problem.
Pos Driver Car Time Gap Laps
1. Fernando Alonso Ferrari 1m48.542s 18
2. Kimi Raikkonen Lotus-Renault 1m48.683s + 0.141s 21
3. Sergio Perez Sauber-Ferrari 1m48.850s + 0.308s 23
4. Kamui Kobayashi Sauber-Ferrari 1m48.863s + 0.321s 20
5. Jenson Button McLaren-Mercedes 1m49.091s + 0.549s 18
6. Felipe Massa Ferrari 1m49.092s + 0.550s 16
7. Mark Webber Red Bull-Renault 1m49.164s + 0.622s 21
8. Romain Grosjean Lotus-Renault 1m49.266s + 0.724s 23
9. Sebastian Vettel Red Bull-Renault 1m49.292s + 0.750s 23
10. Paul di Resta Force India-Mercedes 1m49.382s + 0.840s 22
11. Pastor Maldonado Williams-Renault 1m49.561s + 1.019s 23
12. Lewis Hamilton McLaren-Mercedes 1m49.615s + 1.073s 19
13. Michael Schumacher Mercedes 1m49.621s + 1.079s 26
14. Nico Hulkenberg Force India-Mercedes 1m49.674s + 1.132s 23
15. Jean-Eric Vergne Toro Rosso-Ferrari 1m49.710s + 1.168s 21
16. Daniel Ricciardo Toro Rosso-Ferrari 1m49.776s + 1.234s 22
17. Bruno Senna Williams-Renault 1m50.027s + 1.485s 20
18. Heikki Kovalainen Caterham-Renault 1m52.339s + 3.797s 21
19. Charles Pic Marussia-Cosworth 1m52.566s + 4.024s 20
20. Timo Glock Marussia-Cosworth 1m52.630s + 4.088s 18
21. Vitaly Petrov Caterham-Renault 1m52.809s + 4.267s 22
22. Pedro de la Rosa HRT-Cosworth 1m53.383s + 4.841s 22
23. Narain Karthikeyan HRT-Cosworth 1m53.562s + 5.020s 23
24. Nico Rosberg Mercedes 1m58.113s + 9.571s 5
All timing unofficial