Nico Rosberg of Germany recorded the fastest time in the early session on the fourth day of pre-season testing at the Catalunya circuit here on Sunday morning.
Rosberg steered his Mercedes to a lap time of 1min 20.130sec, three-tenths of a second faster than Ferrari's Fernando Alonso of Spain.
Like his new Mercedes team-mate Lewis Hamilton the previous day, Rosberg set down an impressive marker and stole the thunder from Alonso and triple world champion Sebastian Vettel in the Red Bull on the final day of winter testing.
Another former champion, Jenson Button of Britain, in a McLaren, was third fastest, almost a second slower than Alonso, while Vettel could clock only the seventh fastest lap, more than two seconds slower than the Spaniard.
The new season starts in Melbourne on March 17.
1. Nico Rosberg (GER/Mercedes) 1:20.130, 2. Fernando Alonso (ESP/Ferrari) 1:20.494, 3. Jenson Button (GBR/McLaren-Mercedes) 1:21.444, 4. Nico Hulkenberg (GER/Sauber-Ferrari) 1:21.541, 5. Paul di Resta (GBR/Force India-Mercedes) 1:21.664, 6. Pastor Maldonado (VEN/Williams-Renault) 1:22.415, 7. Sebastian Vettel (GER/Red Bull-Renault) 1:22.514, 8. Charles Pic (FRA/Caterham-Renault) 1:23.115, 9. Jules Bianchi (FRA/Marussia-Cosworth) 1:23.167, 10. Daniel Ricciardo (AUS/Toro Rosso-Ferrari) 1:23.628, 11. Kimi Raikkonen (FIN/Lotus-Renault) 1:25.228