SPA, Belgium -- Nico Rosberg posted the fastest time in the first practice session of the Belgian Grand Prix on Friday, finishing ahead of Mercedes teammate Lewis Hamilton as their intense battle for the Formula One title resumes.

In cool and overcast conditions, Rosberg clocked 1 minute, 51.577 seconds on the 7-kilometre (4.3-mile) Spa track -- the longest on the F1 calendar -- and completed 25 laps. Hamilton, the 2008 champion, did a lap less with a best time of 1:51.674.

Two-time champion Fernando Alonso was third quickest in his Ferrari, with veteran driver Jenson Button fourth best for McLaren.

The F1 championship resumes this weekend following a summer break, and Rosberg leads Hamilton by just 11 points.

Hamilton leads Rosberg 5-4 in race wins this season, but has retired from two races.

Nestled in the Ardennes forest, Spa is also one of the quickest tracks and features famed corners such as Eau Rouge, La Source and Blanchimont.

Former champion Kimi Raikkonen recovered after spinning his Ferrari at La Source, but then had to go back to the pit lane because of temperature problems.

The Finnish driver nevertheless managed the fifth fastest time ahead of the second practice run in the afternoon.