Nick Heidfeld set the fastest time in Saturday's final practice at Spa, outpacing Heikki Kovalianen.
The BMW driver clocked a 1:47.876 on a drying track to beat Kovalainen's time by 0.289s.
Fernado Alonso and Lewis Hamilton were third and fourth, finishing ahead of Ferrari's Felipe Massa who only went out on track in the final five minutes.
Report: Heavy overnight rain meant that not only was the track damp at the start of final practice but any rubber laid down on Friday had been washed away, leaving the track slippery. A light rain started to fall on parts of the circuit as the session got underway with the air and track temperature sitting at 16'C.
Giancarlo Fisichella, Nick Heidfeld and Adrian Sutil were the first drivers out, leading a train that included all the drivers barring the two Ferraris.
Jenson Button's session lasted a total of three minutes and not even a complete lap as the Brit's Honda came to a halt on the Kemmel straight, bringing out the yellow flags.
A break in the track activity was finally broken by Heidfeld, who set the first timed lap of the session. He clocked a 2:00.227, which was eclipsed seconds later by Bourdais who went six tenths up. Seb Vettel could only manage a 2:02.488, putting him third with Sutil and Fisichella fourth and fifth.
Timo Glock went P1 with a 1:58.6, narrowly edging the Renault of Fernando Alonso by 0.02s. Nelson Piquet Jr, though, dropped both drivers when he went quickest only to be beaten by Mark Webber in a Red Bull.
Glock returned to the P1 slot while his team-mate Jarno Trulli took seventh place on his first lap. David Coulthard was the next to go top only to be beaten by Heidfeld seconds later.
Halfway through the session all the drivers barring the Ferraris had at least gone out although only 12 had set times.
A drying track saw Vettel set two fastest sectors times to hit the front with a 1:55.192, almost two seconds up on Heidfeld's best. This prompted a move from Glock and Kazuki Nakajima to switch to the dry tyres.
Glock went second quickest despite a lock up at La Source, however, three fastest sector times saw him take the P1 slot on the following lap with a 1:52. Nakajima went second before improving to first. He soon lost out to Rosberg.
With twenty minutes on the clock Kimi Raikkonen made his first appearance out on track taking sixth place while Glock and Rosberg continued to battle for first place. Raikkonen had a moment at the Bus Stop, outbraking himself and going on straight.
Bourdais was the next in line to go top as the drying track meant that lap times continued to tumble. Robert Kubica broke into the 1:449s to hit the front before being surpassed by Alonso and Piquet Jr and then Lewis Hamilton, who clocked a 1:48.35 on his first lap while Heikki Kovalainen went second.
Felipe Massa could only manage tenth place on his first timed lap, which was set with just five minutes left in practice. His team-mate Raikkonen jumped up to second place but was still half a second off Hamilton's P1 time.
Heidfeld, though, dropped both drivers when he posted a 1:47.876 to take the P1 slot while Kovalainen took second place with Alonso going P3.
Times
01 N. Heidfeld BMW 1:47.876 19 laps
02 H. Kovalainen McLaren 1:48.165 10 laps
03 F. Alonso Renault 1:48.307 19 laps
04 L. Hamilton McLaren 1:48.356 10 laps
05 F. Massa Ferrari 1:48.692 6 laps
06 S. Vettel Scuderia Toro Rosso 1:48.768 16 laps
07 K. Räikkönen Ferrari 1:48.815 10 laps
08 N. Rosberg Williams 1:48.836 13 laps
09 N. Piquet jr. Renault 1:48.946 17 laps
10 M. Webber Red Bull 1:49.054 14 laps
11 J. Trulli Toyota 1:49.057 16 laps
12 D. Coulthard Red Bull 1:49.125 11 laps
13 R. Kubica BMW 1:49.250 12 laps
14 S. Bourdais Scuderia Toro Rosso 1:49.256 19 laps
15 T. Glock Toyota 1:49.535 18 laps
16 K. Nakajima Williams 1:49.830 12 laps
17 G. Fisichella Force India F1 1:49.949 16 laps
18 A. Sutil Force India F1 1:50.034 16 laps
19 R. Barrichello Honda 1:50.061 17 laps
20 J. Button Honda no time 1 laps
