Max Verstappen led a surprise Red Bull one-two in second practice for Sunday's Belgian Grand Prix as Formula One roared back into life following its summer shutdown.
Nico Rosberg set the pace on Friday morning ahead of Lewis Hamilton, who will serve at least a 30-place grid penalty for exceeding the number of permitted changes to his Mercedes engine this season.
But Rosberg was only sixth on Friday afternoon, one second slower than Verstappen's best lap of one minute and 48.085 seconds, while Hamilton, who will start Sunday's race from the back of the field, 13th.
The curious result is likely to be a knock-on effect from Hamilton's penalty. With his result in Saturday's qualifying now meaningless given his mammoth penalty, Hamilton would have turned his attention to his race pace in a bid to provide him with the best opportunity of storming back through the field.
Nevertheless, Red Bull will be boosted by their strong form here with Daniel Ricciardo one quarter of a second slower than Belgium-born Verstappen. Nico Hulkenberg was third for Force India and Ferrari's Sebastian Vettel - the only other driver within one second of Verstappen - in fourth place.
While the Belgian Grand Prix is often synonymous with inclement weather, the longest circuit on the Formula One calender was bathed in sunshine as unseasonably warm temperatures continued to sweep through the Ardennes on Friday.
But the unusually settled weather is unlikely to please Hamilton who would have preferred rather more mixed-up conditions given his penalty plight.
Elsewhere, Jenson Button was eighth for McLaren while his team-mate Fernando Alonso, who will join Hamilton on the back row after being hit with a 35-place penalty for using more engine parts than permitted, was 12th fastest.
British rookie Jolyon Palmer is bidding to prove to his Renault bosses that he deserves a second season in the sport, but mechanical issues blighted both of his practice sessions here. He finished the session in 20th, two tenths of a second slower than team-mate Kevin Magnussen.
Earlier on Friday, Rosberg and Ricciardo were also among a number of drivers to trial the Halo during opening practice.
Plans for the controversial cockpit protection device to become mandatory in the sport have been shelved until 2018 following a meeting of F1's strategy group last month.
But the Halo will continue to be tested, with the device attached to Rosberg, Ricciardo, Hulkenberg and Carlos Sainz's cars on Friday.