Nico Rosberg was fastest ahead of Mercedes team-mate Lewis Hamilton in an uneventful first practice session at the Belgian Grand Prix on Friday.

Rosberg is 19 points behind Hamilton in the battle for the Formula One world title, but Mercedes confirmed ahead of FP1 that the Brit will take a 15-place grid penalty at Spa-Francorchamps after having a sixth different power unit of the season fitted.

German Rosberg, also using a new power unit but not facing a penalty as he has not exceeded his quota of five, laid down a marker by clocking a quickest lap of one minute 48.348 seconds.

Hamilton was 0.730secs off the pace, while Ferrari's Kimi Raikkonen was third and Force India's Sergio Perez was also within a second of Rosberg.

Rosberg and Red Bull's Daniel Ricciardo were among the drivers to test the 'halo' safety equipment during a frustrating first session for Fernando Alonso.

The Spaniard was unable to set a time as McLaren worked on technical issues on his new Honda power unit.

Frenchman Esteban Ocon, making his F1 debut for Manor, was an encouraging 16th on the timesheets but had one moment to forget when he drove over a cone in the pits.