Rosberg's Mercedes quickest in Bahrain testing
Mercedes AMG Petronas driver Nico Rosberg of Germany takes a pit stop during the Formula One Bahrain Grand Prix at Sakhir circuit in Manama on April 6, 2014 - by Patrick Baz
The 28-year-old German, who finished second to Mercedes teammate Lewis Hamilton in a race rated as the most exciting for years, topped the times, recording a best lap of 1min 35.667.
That was 2.5 seconds slower than the time he set to claim pole for Sunday's grand prix.
Nico Hulkenberg drove his Mercedes-powered Force India into second in the times, four tenths behind Rosberg, with Fernando Alonso's Ferrari six tenths away in third.
World champions Red Bull, with Daniel Ricciardo on the track, took seventh after completing 91 laps.
Hamilton, who with the win in Bahrain moved up to within 11 points of Rosberg in the F1 drivers' standings, takes the wheel for Mercedes for the second day of testing on Wednesday.
The 2014 championship then moves on to China for the fourth leg of the season on April 20.
Bahrain testing times
1.Nico Rosberg (GER/Mercedes) 1:35.697 (121 laps), 2.Nico Hülkenberg (GER/Force India) 1:36.064 (69), 3.Fernando Alonso (ESP/Ferrari) 1:36.626 (68), 4. Kevin Magnussen (DEN/McLaren)Merce 1:36.634 (102), 5.Valtteri Bottas (FIN/Williams) 1:37.305 (28), 6. Max Chilton (GBR/Marussia) 1:37.678 (60), 7.Daniel Ricciardo (AUS/Red Bull) 1:38.326 (91), 8. Sergueï Sirotkin (RUS/Sauber) 1:39.023 (76), 9. Robin Frijns (NED/Caterham) 1:40.027 (62), 10. Pastor Maldonado (VEN/Lotus) 1:40.183 (16), 11.Daniil Kvyat (RUS/Toro Rosso) 1:40.452 (67)