Nico Rosberg, who has yet to transform his practice pace into anything higher than sixth place in a race this season, topped the timesheets at the Bahrain Grand Prix.

The German, son of 1982 champion Keke, lapped the Sakhir circuit in a time of 1min 33.339sec to edge out Renault's Fernando Alonso, who was second fastest in the afternoon.

Rosberg has now been quickest in seven of the 11 practice sessions this year. Reigning champion Lewis Hamilton was fastest in the morning with his time of 1:33:647 only beaten by Rosberg, Alonso and Toyota's Jarno Trulli in the later session.

Red Bull's Sebastian Vettel, winner of the last race in China, was fourth fastest in the second session ahead of Australian team mate Mark Webber and Brawn GP's championship leader Jenson Button.

BMW-Sauber had filled second and third place on a hot and overcast morning with Germany's Nick Heidfeld ahead of Poland's Robert Kubica. The top three cars in that session all had the new KERS energy recovery system, that offers drivers an extra boost of power at the push of a button, at a circuit where it is expected to be a real advantage.

McLaren, who said at the start of the season their car was still some way off becoming a winner, have made changes to it ahead of the Bahrain race.

Hamilton's team-mate Heiki Kovalainen said: “We have a few modifications for the floor, hopefully a little bit more downforce, but nothing dramatic.”