Montmel - Germany's Mercedes star Nico Rosberg followed up his Spanish Grand Prix win last Sunday by setting the fastest time on the first session of two days of private testing at the Circuit de Catalunya.
Rosberg was a full two seconds faster than his closest rival Ferrari's Raffaele Marciello and almost three seconds ahead of third placed Pastor Maldonado of Lotus.
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The German, second in the world standings 20 points behind teammate Lewis Hamilton after five Grand Prix, also put in 78 laps, 24 more than Marciello.
A further nine drivers will get a run out in a later session Tuesday.
1. Nico Rosberg (GER/Mercedes-AMG) 1:24.374 (78 laps)
2. Raffaele Marciello (ITA/Ferrari) 1:26.648 (54 laps)
3. Pastor Maldonado (VEN/Lotus-Mercedes) 1:27.338 (53 laps)
4. Daniil Kvyat (RUS/Red Bull-Renault) 1:27.684 (20 laps)
5. Pierre Gasly (FRA/Toro Rosso-Renault) 1:28.147 (60 laps)
6. Marcus Ericsson (SWE/Sauber-Ferrari) 1:28.803 (37 laps)
7. Nick Yelloly (GBR/Force India-Mercedes) 1:28.856 (49 laps)
8. Oliver Turvey (GBR/McLaren-Honda) 1:29.730 (31 laps)
9. Felipe Massa (BRA/Williams-Mercedes) 1:30.433 (33 laps)