Rosberg leads the way at Valencia

The Williams driver outpaced McLaren's Pedro de la Rosa by two tenths of a second, as his team continued to put mileage on the seamless shift gearbox that they hope they will be able to start the season with.

Despite being edged out in the timesheets, de la Rosa was overjoyed with the performance of the latest spec Mercedes-Benz engine as he began a programme to evaluate its reliability.

The Spaniard completed a total of 146 laps and is hoping to complete two full race distances by tomorrow morning, after which Kimi Raikkonen will take over the car.

Speaking to autosport.com, de la Rosa could not hide his delight with the latest findings.

"This is the latest spec engine (for Bahrain)," he said. "The engine is definitely getting better. I am not saying it is perfect, but we are going in the right direction and I am happy - although I will be happier when we complete the two race distances."

Mark Webber was third fastest but suffered two mechanical problems during the course of the day.

Heikki Kovalainen only managed to complete 54 laps to set the fourth quickest time, bringing out the red flags once just before lunch, while Gary Paffett spent the day in the orange MP4-20.

He brought the red flags out at 3.30pm after deliberately running the car dry during fuel consumption tests.

Today's times:

Pos  Driver        Team                      Time      Laps
 1.  Rosberg       Williams-Cosworth    (B)  1:11.030   85
 2.  de la Rosa    McLaren-Mercedes     (M)  1:11.238  146
 3.  Webber        Williams-Cosworth    (B)  1:11.327   67
 4.  Kovalainen    Renault              (M)  1:11.450   54
 5.  Paffett       McLaren-Mercedes     (M)  1:13.055   71

All Timing Unofficial