Vettel’s best was 0.6s down on Hamilton, and the German was backed up by newly re-signed team mate Kimi Raikkonen in fourth. Sergio Perez took fifth for Force India, followed by the Red Bulls of Daniel Ricciardo and Daniil Kvyat, and team mate Nico Hulkenberg. Williams’ Valtteri Bottas and Felipe Massa completed the top ten.
It proved to be a tough session for McLaren, who already face the prospect of starting from the back of the grid due to penalties. Fernando Alonso failed to set a time and managed just one lap thanks to suspected exhaust problems, while team mate Jenson Button finished 17th, trailed only by the two Marussias.
It was Red Bull who led the switch onto the faster, soft tyres, and Ricciardo and Kvyat duly hit the front, posting 1m 49.930s and 1m 49.980s respectively. Max Verstappen also elected to make an early change for the yellow-marked rubber, and for a time occupied third for Toro Rosso on 1m 50.599s.
At that stage Hamilton was the fastest runner on mediums with 1m 50.635s, before Vettel fired a shot across Mercedes’ bows with 1m 50.460s.
That left the order Ricciardo, Kvyat, Vettel, Verstappen, Hamilton, Raikkonen (1m 50.707s) and Rosberg (1m 50.821s) going into the final 10 minutes. But that’s when the serious stuff happened.
First Rosberg clocked 1m 49.482s on softs, but Hamilton immediately smashed that with 1m 48.984s to move ahead of his team mate for the first time this weekend. Vettel jumped to third with 1m 49.629s, while Raikkonen slotted into fourth with 1m 49.864s, which came in spite of traffic. The Finn then set the best sector one time, but promptly lost a second and a half to Hamilton in sector two; Vettel, meanwhile, was also pushing hard enough to run wide at Les Combes. Neither went quicker.
Perez very nearly ousted Raikkonen with 1m 49.866s, which was good enough to demote Ricciardo and Kvyat, whose focus had turned to long runs. Hulkenberg, meanwhile, jumped up to eighth with a very neat lap of 1m 50.000s, which left him a few tenths clear of Bottas and Massa. The Williams pair only really got going in the final 20 minutes of the session, and managed 1m 50.179s and 1m 50.447s respectively.
Carlos Sainz ended up Toro Rosso’s faster runner, in part because Verstappen had switched to his own long-run simulation on the softs. The Spaniard posted 1m 50.552s for 11th, ahead of Lotus’s Pastor Maldonado on 1m 50.585s. Verstappen was up next, with Felipe Nasr in the lead Sauber one spot further back in 14th, on 1m 50.690s.
Marcus Ericsson took the sister C34 round in 1m 51.054s to head Romain Grosjean on 1m 51.187s for Lotus and Button who couldn’t better 1m 51.981s in the McLaren. That left the closely matched Marussias of Will Stevens and Roberto Merhi 18th and 19th, on 1m 54.262s and 1m 54.281s respectively.
There were several minor offs and spins during the session, while Pirelli also confirmed mid-way through the hour that overnight investigations into Rosberg's tyre failure in FP2 had revealed 'no structural integrity issue,' pointing instead to an external cut being the cause of the incident.