World championship leader Nico Rosberg ended the opening day of practice for tomorrow's Bahrain Grand Prix at the top of the timesheets ahead of Mercedes team-mate Lewis Hamilton, even as rivals Ferrari hit trouble.
Rosberg, winner of the season-opening Australian Grand Prix, lapped the floodlit 5.4-kilometer long Sakhir circuit in one minute 31.001.
That was good enough for the German to end the day two-tenths of a second clear of Hamilton after having also led the Briton in the opening afternoon session.
Ferrari were hoping to take the battle to Mercedes this weekend in Bahrain after having run the reigning champions close at the season-opener in Australia. But the best the Maranello-based squad could manage yesterday was fifth and sixth with Kimi Raikkonen slightly ahead of Sebastian Vettel.
Neither of the pair managed a clean run on their fastest laps with Vettel making a mistake on his flier while Raikkonen's fastest lap was ruined by traffic.
The German was later forced to grind to a halt as the nut on his left-rear wheel was not on, bringing an end to his session with 15 minutes still to run.
The duo had also completed the least amount of laps in the opening afternoon session and ended the day about a second-and-a-half adrift of Rosberg's best. Jenson Button ended the day third for McLaren ahead of Toro Rosso's Max Verstappen.
McLaren reserve Stoffel Vandoorne, standing in for the injured Fernando Alonso, was eleventh fastest, seven-tenths slower than his world champion team-mate at the end of a solid opening day of practice.
Daniil Kvyat was seventh for Red Bull ahead of Valtteri Bottas in the Williams. His team-mate Daniel Ricciardo was ninth ahead of the second Williams of Felipe Massa who rounded out the top-ten.