Rosberg quickest in Bahrain Formula One testing
Mercedes' German Nico Rosberg waves during the Formula One pre-season test days at Jerez racetrack in Jerez on January 31, 2014 - by Jorge Guerrero
Rosberg managed to go a second faster than his teammate Lewis Hamilton a day earlier, outpacing Jenson Button in a Mclaren-Mercedes and Kimi Raikkonen in a Ferrari.
Brazilian Felipe Nasr, a new test driver with the Williams team, took to the wheel for the first time and was fourth-quickest.
A final pre-season testing session will take place in Bahrain next Thursday, February 27, before the first race of the season, the Australian Grand Prix in Melbourne, on March 16.
Mercedes go into Melbourne in good shape after strong testing both in Bahrain and in Jerez in Spain last month.
For world champions Red Bull, who endured a torrid time testing in Jerez, things looked a little brighter, with Sebastian Vettel's new teammate Daniel Ricciardo coming in 7th in Bahrain.
However, he was still a full six seconds off the pace set by Rosberg and Mercedes as Red Bull continued to struggle with technical issues.
Saturday testing times
1. Nico Rosberg (GER/Mercedes-AMG) 1min 33.283sec, 2. Jenson Button (GBR/McLaren-Mercedes) 1:34.957, 3. Kimi Räikkönen (FIN/Ferrari) 1:36.718, 4. Felipe Nasr (BRA/Williams-Mercedes) 1:37.569, 5. Pastor Maldonado (VEN/Lotus-Renault) 1:38.707, 6. Sergio Perez (MEX/Force India-Mercedes) 1:39.258, 7. Daniel Ricciardo (AUS/Red Bull-Renault) 1:39.837, 8. Jean-Eric Vergne (FRA/Toro Rosso-Renault) 1:40.472, 9. Kamui Kobayashi (JPN/Caterham-Renault) 1:43.027, 10. Marcus Ericsson (SWE/Caterham-Renault) 1:45.094