Jenson Button put a brave face on his failure to register a lap in qualifying before his McLaren-Honda broke down in Bahrain.
Both Mercedes drivers in top 3 splitted by Ferrari's Vettel.
World champion Lewis Hamilton beat Ferrari rival Sebastian Vettel to the quickest time in final practice for the Bahrain Grand Prix.
Renault's technical chief Rob White admits that Red Bull and Toro Rosso are still vulnerable to power unit failures in the Bahrain Grand Prix as the company has not been able to address all of the causes of the problems in China.
As in China last Friday the Third and Reserve Driver for Lotus F1 Team took over duties behind the wheel from Romain Grosjean in FP1.
Sebastian Vettel: "It’s hard to say if we got closer to Mercedes, everybody seemed to be closer to them but I’m sure they didn’t show everything today."
The E23 Hybrid showed good potential; it was well balanced and reliable with scope for improved pace.
Nico Rosberg beat Mercedes teammate Lewis Hamilton to the quickest time of the day in second practice for the Bahrain Grand Prix.
German edges his teammate by one tenth, both Ferrari behind them with Raikkonen in P3. Teams were working through their tyre programs.
Mercedes non-executive chairman Niki Lauda says he is not concerned that Lewis Hamilton has yet to sign his new contract for 2016 and beyond, and insists that the deal is done and dusted.
Ferrari ends the session 1-2 with Williams' Bottas in third.
Kimi Raikkonen set the fastest time in free practice one for the Bahrain Grand Prix, leading a Ferrari one-two as the Mercedes cars languished near the bottom of the timesheets.
Felipe Massa says that Ferrari is doing a much better job with the 2015 Pirelli tyres than any other team – and that Williams has to work hard to catch up.
Fernando Alonso insists that a lack of power is not masking any unexpected deficiencies in the McLaren chassis – in other words he expects its handling to remain consistent as the engine performance is ramped up.