Formula One's practice king this season again ruled the roost ahead of Sunday's Spanish Grand Prix.

For the eighth time in 14 sessions over the course of the year, it was Nico Rosberg driving a Grove-built AT&T Williams who topped the timesheets.

Come the end of the second 90-minute session at Barcelona's Circuit de Catalunya, the 23-year-old had set the fastest time of the day overall with a lap of one minute 21.588secs.

But Rosberg did not have it all his own way because just minutes prior to the session coming to a close, he was forced to trundle off the track and park his car on the grass due to an apparent electrical problem.

Despite that issue, it proved to be a productive day for Williams as Kazuki Nakajima was second quickest, just 0.152secs adrift of his team-mate.

Williams' concern this season, though, is they have yet to transfer their practice pace into a decent qualifying performance or race result.

Rosberg has managed just 3.5 points so far, with his best finish a sixth in the season-opening Australian Grand Prix, whilst Nakajima has yet to get off the mark.

Behind the Williams duo it was Fernando Alonso in his Enstone-built Renault Renault as he gave his fans something to cheer, followed by Rubens Barrichello for Brackley's Brawn GP and Red Bull Racing's Mark Webber.

Championship leader Jenson Button, quickest in first practice with a time that proved to be the third best of the day, was sixth in the second session, narrowly ahead of one of his main title rivals in Red Bull's Sebastian Vettel.

As for the big guns, Kimi Raikkonen headed that particular list, but hardly something to be proud of as he was tenth for Ferrari. Current world champion Lewis Hamilton was down in 13th.