Rapidly improving Valtteri Bottas of Williams outpaced the previously dominant Mercedes men in Saturday morning’s third and final free practice session ahead of Sunday’s Belgian Grand Prix.
The 24-year-old Finn, who qualified on the front row of the grid in Austria in June, clocked a best lap of one minute and 49.465 seconds to wind up fastest ahead of Australian Daniel Ricciardo of Red Bull by 0.268 seconds.
Championship leader German Nico Rosberg was third quickest in the leading Mercedes, seven-tenths of a second down on Bottas, ahead of four-time winner Finn Kimi Raikkonen of Ferrari and Briton Lewis Hamilton, who was down in fifth in the second Mercedes.
Two-time champion Fernando Alonso of Spain was sixth in the second Ferrari after a final flurry of action on soft tyres shuffled the pack on a drying, but mostly dismal morning in the Belgian Ardennes where overnight rain had left the circuit in a soggy condition.
On a circuit that lived up to the local reputation of providing changeable conditions, there was little significant activity until the final 10 minutes when it appeared that the Mercedes team were content to run within their themselves and keep their top pace for the afternoon qualifying session.
Russian rookie Daniil Kvyat was seventh for Toro Rosso ahead of Briton Jenson Button of McLaren, Brazilian Felipe Massa in the second Williams and the luckless Frenchman Jean-Eric Vergne, who was told this week that he will be out of the team next year to make way for the arrival of 16-year-old Dutch racer Max Verstappen.