The German, 19 points down in the title race, lapped the Spa-Francorchamps circuit in 1:48.348, some 0.730 quicker than Lewis Hamilton.
However, both the Mercedes used a set of SuperSoft tyres to post their quickest times, with a delta of around 0.8 to the soft tyre, which Kimi Raikkonen used to steer his Ferrari to P3, 0.069 down on Hamilton.
Sergio Perez capped off a fine morning for Force India, by slotting into P4, ahead of Sebastian Vettel, the two Red Bull’s of Daniel Ricciardo and Max Verstappen. Nico Hulkenberg made it two Force India’s in the top eight.
Valterri Bottas and Esteban Gutierrez rounded out the top 10, in blistering heat in the Ardennes forest.
Barely, 24 hours after saying that the difference in Honda’s approach from 2015 to 2016 was “night and day”, Fernando Alonso was unable to set a timed lap, as his PU developed a water leak, limiting him to just three install laps.
Down at Manor, single-seater veteran, 19 year-old Esteban Ocon ended his first official session as a race driver in P16, nearly 1s faster than new teammate Pascal Wehrlein. 1-0 to the Frenchman, in what could be race to replace Hamilton or Rosberg at Mercedes one day.
Halo and prototype testing takes centre stage
Introduction of cockpit head protection has been delayed until 2018, so that further tests can be done. That includes running in official practice sessions. This time, Rosberg, Hulkenberg, Ricciardo and Carlos Sainz were the four to test the halo device, with a few install laps the furthest it got, aside from on Rosberg’s car.
The German completed the first flying lap, in F1 history with head-protection, a 1:49.481 to jump to P1, setting the early pace in the process.
Just after the half-hour mark, the SuperSoft was fitted to the W07, and Rosberg quickly set the 1:48.348 that would see him eventually top the session, Hamilton’s response was quick to follow but was well-down on the benchmark.
A possible reason for this, is the World Champion’s W07 is being set up for slipstreaming and overtaking, (less rear-wing, and downforce) as he is going to take an engine penalty. Mercedes confirmed that he will be taking a sixth MGU-H and Turbo, exceeding the permitted limit of five for the season. Most of the deficit is being lost in the twisty second sector.
To increase the pool of engines available to him, Mercedes are expected to take another engine, and consign Hamilton to a P22 start, with a world-record 75 place grid penalty, breaking Jenson Button’s effort of 55 12 months ago.
Pirelli also were testing prototype tyres for the future, indicated by uncoloured side-walls on the tyres. Perez was amongst those to test the rubber, before he reverted to the Soft tyre, and posted the fourth fastest time, at a circuit he briefly led the race at last year.
Yet more Renault trouble
Jolyon Palmer, who eventually finished P21, experienced suspension issues on his Renault RS16, which ended his session earlier than most, teammate Kevin Magnussen capped off a below-par session for the Enstone team, ending up P20.
An initial lack of grip caught out Verstappen early on, quickly righting his RB12, before Romain Grosjean and Marcus Ericsson both ran wide a Stavelot, with the Frenchman going for a trip through the gravel, whilst teammate Gutierrez reported brake issues throughout the opening 90 minutes.
Sauber also announced that Ericsson would be taking a 10 place grid penalty, as he will be taking a sixth turbo element of the season.
Belgian Grand Prix – First Practice times:
1. Nico Rosberg – Mercedes – 1:48.348
2. Lewis Hamilton – Mercedes +0.730
3. Kimi Raikkonen – Ferrari +0.799
4. Sergio Perez – Force India +0.926
5. Sebastian Vettel – Ferrari +1.420
6. Daniel Ricciardo – Red Bull +1.434
7. Max Verstappen – Red Bull +1.517
8. Nico Hulkenberg – Force India +1.740
9. Valtteri Bottas – Williams +2.046
10. Esteban Gutierrez – Haas +2.235
11. Romain Grosjean – Haas +2.551
12. Felipe Massa – Williams +2.774
13. Marcus Ericsson – Sauber +2.777
14. Carlos Sainz – Toro Rosso +3.076
15. Felipe Nasr – Sauber +3.420
16. Esteban Ocon – Manor +3.439
17. Danill Kvyat – Toro Rosso +3.960
18. Jenson Button – McLaren +4.059
19. Pascal Wehrlein – Manor +4.489
20. Kevin Magnussen – Renault +4.705
21. Jolyon Palmer – Renault +4.741
22. Fernando Alonso – McLaren – No time