Alonso, who has never won the Belgian Grand Prix, clocked a best time of 1:55.198s on the harder compound tyre as the circuit began to dry out in the middle sector with around 15 minutes remaining. Force India’s Paul di Resta was second fastest from team-mate Adrian Sutil with Sergio Perez fourth and Nico Rosberg fifth.
With a fine misty rain falling at the start of the session, teams opted for the intermediate tyre but with the circuit still fairly dry in parts the rears began graining after only six or seven laps.
There was no shortage of incident as several drivers including Kiki Raikkonen and Sebastian Vettel sliding into the damper Bus Stop chicane and Turn 1.
Red Bull were the first to experiment with the dry compound with about 40 minutes remaining and as the rain eased off further, so the lap times tumbled – Mark Webber, Vettel, Lewis Hamilton, Rosberg, Perez, Di Resta and Jenson Button all swapping times at the top.
But Lotus did not have such a good time of things. The team experimented with their new passive DRS system but it didn’t seem to make a huge difference, Raikkonen and Romain Grosjean finishing bottom of the times.
Raikkonen also experienced a big wobble at Blanchimont with a defective front right hub thought to be to blame. And Hamilton did well to avoid hitting Esteban Gutierrez into the Bus Stop chicane as the Sauber broke suddenly in front of his Mercedes.
The famous Spa rain returned in the final 10 minutes but not enough to return to intermediates and so Alonso’s time remained unbeaten.