Nico Rosberg topped opening practice for the Belgian Grand Prix as Formula 1 returned from its summer break at Spa-Francorchamps.
Rosberg arrived in Belgium trailing Mercedes teammate Lewis Hamilton by 19 points in the drivers' championship, but enjoyed the edge on the Briton in opening practice on Friday morning.
Rosberg recorded a fastest lap time of 1:48.348 on the super-soft tyre and with the 'Halo' cockpit protection device fitted to his car in the early part of the session.
Rosberg was joined by Daniel Ricciardo, Nico Hulkenberg and Carlos Sainz Jr. in conducting running with the Halo, marking its most extensive test yet as evaluation ahead of a possible introduction in 2018 continues.
Hamilton completed a one-two for Mercedes in FP1, finishing three-quarters of a second behind Rosberg at the top of the timesheets.
Four-time Belgian Grand Prix winner Kimi Raikkonen finished the session third for Ferrari, with teammate Sebastian Vettel in P5. Force India's Sergio Perez split the duo, finishing nine-tenths of a second off Rosberg's benchmark.
Red Bull failed to match Ferrari for pace in FP1, finishing sixth and seventh with Daniel Ricciardo and Max Verstappen. Nico Hulkenberg was eighth in the second Force India, while Valtteri Bottas and Esteban Gutierrez rounded out the top 10 for Williams and Haas respectively.
Esteban Ocon impressed during his first outing for Manor after replacing Rio Haryanto, finishing P16 and over a second clear of teammate Pascal Wehrlein.
It proved to be a session to forget for McLaren as Fernando Alonso was limited to just three laps in total, failing to record a lap time. Teammate Jenson Button was classified 18th overall, four seconds behind Rosberg at the top.