There are many wise judges tipping Nico Rosberg to break Sebastian Vettel's monopoly of the Formula One drivers' world championship this year and the news from Bahrain on Saturday gave them further encouragement.

Mercedes have the best car – at least for the moment – and Rosberg's more analytical approach to a new and very complex technology is thought to have greater potential than the faster, more instinctive style of Lewis Hamilton, who might struggle to match his team-mate's consistency even though he will doubtless blow everyone else away on occasions.

Certainly Rosberg looked impressive on the last day of the second testing session in Bahrain. His time of 1min 33.283sec was the fastest of the test and beat everyone else by 1.627sec, lending further credence to the favourable impression created in the first test in Spain last month. Mercedes had also been the dominant team in Bahrain on Friday.

On Saturday morning, when Mercedes concentrated on one-lap simulations, Rosberg put in his flyer, using Pirelli's soft rubber. But reliability is the essence of this year's testing and in the afternoon the German returned to complete more than 50 laps, making it 89 for the day.

McLaren also look strong this year, if well short of Mercedes, and Jenson Button was second fastest on Saturday , with Kimi Raikkonen third for Ferrari.

But Red Bull are still struggling, and with eight of the 12 testing days now over they will be desperate to turn things round when they return to Bahrain next week. They are six seconds slower than Mercedes, and although test timings are often misleading that is some margin to make up.

Yesterday Daniel Ricciardo completed just 15 laps and the RB10 spent most of the day in intensive care with Red Bull mechanics attempting to revive it.

"In all honesty it wasn't a great day," said Ricciardo. Race engineering co-ordinator Andy Damerum said: "On Daniel's install we noticed a software problem and that knocked us back for the morning. Then we had to abort a lunchtime run because we had a mechanical issue. We brought Daniel back in and discovered some damage which was worse than we imagined." Time is running out for the four-times double champions.