Jenson Button takes pole at Spa in dramatic Belgian GP qualifying session

Kamui Kobayashi claimed his maiden front-row start as he underlined Sauber's speed with a shock second place, while world champion Sebastian Vettel failed to make it out of Q2.

Button put himself eight tenths clear of the field for much of Q2, then repeated that speed to deliver a 1m47.686s early in Q3.

One of the few drivers to do two Q3 runs, he found even more time at the second attempt and delivered a 1m47.573s.

Kobayashi was three tenths adrift as he secured his career-best Formula 1 start. Team-mate Sergio Perez also shone in fifth place.

Q1 pacesetter Pastor Maldonado was another star underdog as he took third for Williams, although an impeding incident involving the Venezuelan and 12th-place qualifier Nico Hulkenberg is under investigation.

Pre-race favourite Lotus only managed fourth with Kimi Raikkonen and ninth with Romain Grosjean. The latter had a few scares just getting out of Q1 following a mistake and traffic issues with an HRT.

World championship leader Fernando Alonso could not repeat his morning practice performance and starts sixth.

As one McLaren took pole, the other was only eighth quickest, although Lewis Hamilton will gain a place when Mark Webber's Red Bull is demoted five places from seventh due to a gearbox change penalty.

Force India's Paul di Resta completed the top 10.

Vettel was the most significant casualty of a close Q2. Just two tenths separated him from Red Bull team-mate Webber, but that translated to seven positions, as last year's Spa poleman and race winner ended up only 11th, 0.012s off a Q3 spot.

He was not the only big name to miss out. Felipe Massa trailed the sister Ferrari of Alonso by seven tenths as he struggled to 14th, behind Michael Schumacher, whose 13th place was the best Mercedes could manage on a tough afternoon.

Already carrying a five-place grid penalty for a gearbox change following his morning failure, Nico Rosberg was only 18th in qualifying after crossing the line moments too late for a final Q1 run.

Rosberg's disappointment meant both Toro Rossos reached Q2, where they beat the Williams of Bruno Senna. The Brazilian pulled off an incredible save after sliding broadside across the kerbs through most of Pouhon, then had to pit for repairs and could not get above 17th when he rejoined.

At the back, Timo Glock used Marussia's upgrades to get a little closer to the Caterhams, but his team-mate Charles Pic was beaten to 22nd by Pedro de la Rosa's HRT.

                                             
Pos  Driver              Car                   Time       Gap
 1.  Jenson Button       McLaren-Mercedes      1m47.573s
 2.  Kamui Kobayashi     Sauber-Ferrari        1m47.871s  + 0.298s
 3.  Pastor Maldonado    Williams-Renault      1m47.893s  + 0.320s
 4.  Kimi Raikkonen      Lotus-Renault         1m48.205s  + 0.632s
 5.  Sergio Perez        Sauber-Ferrari        1m48.219s  + 0.646s
 6.  Fernando Alonso     Ferrari               1m48.313s  + 0.740s
 7.  Mark Webber         Red Bull-Renault      1m48.392s  + 0.819s***
 8.  Lewis Hamilton      McLaren-Mercedes      1m48.394s  + 0.821s
 9.  Romain Grosjean     Lotus-Renault         1m48.538s  + 0.965s
10.  Paul di Resta       Force India-Mercedes  1m48.890s  + 1.317s
Q2 cut-off time: 1m48.993s                                Gap *
11.  Sebastian Vettel    Red Bull-Renault      1m49.722s  + 0.472s
12.  Nico Hulkenberg     Force India-Mercedes  1m49.362s  + 0.112s
13.  Michael Schumacher  Mercedes              1m49.742s  + 0.492s
14.  Felipe Massa        Ferrari               1m49.588s  + 0.338s
15.  Jean-Eric Vergne    Toro Rosso-Ferrari    1m49.763s  + 0.513s
16.  Daniel Ricciardo    Toro Rosso-Ferrari    1m49.572s  + 0.322s
17.  Bruno Senna         Williams-Renault      1m49.958s  + 0.708s
Q1 cut-off time: 1m50.126s                                Gap **
18.  Nico Rosberg        Mercedes              1m50.181s  + 1.188s***
19.  Heikki Kovalainen   Caterham-Renault      1m51.739s  + 2.746s
20.  Vitaly Petrov       Caterham-Renault      1m51.967s  + 2.974s
21.  Timo Glock          Marussia-Cosworth     1m52.336s  + 3.343s
22.  Pedro de la Rosa    HRT-Cosworth          1m53.030s  + 4.037s
23.  Charles Pic         Marussia-Cosworth     1m53.493s  + 4.500s
24.  Narain Karthikeyan  HRT-Cosworth          1m54.989s  + 5.996s

107 per cent time: 1m56.622s

* Gap to fastest in Q2
** Gap to fastest in Q3
*** Will take five-place penalty