Istanbul - Williams driver Nico Rosberg posted the fastest time in the first free practice session ahead of Sunday's Turkish Grand Prix in Istanbul.

World champion Lewis Hamilton was second fastest in a McLaren- Mercedes ahead of Toyota's Jarno Trulli and Sebastian Vettel in a Red Bull.

Overall leader Jenson Button, who has won five of the season's six races, was 11th, two places behind his Brawn GP team-mate Rubens Barrichello.

Germany's Rosberg posted 1 minute 28.952 seconds on the 5.338- kilometre Istanbul Park circuit, with Britain's Hamilton 0.311 seconds back on 1:29.263 and Italy's Trulli on 1:29,271.

Ferrari's Felipe Massa, who has won in Istanbul from pole position for the past three years, was fifth fastest in the session.

Team-mate Kimi Raikkonen was seventh, a place behind Kazuki Nakajima in a Williams and one ahead of Renault's Fernando Alonso.

Ferrari are hoping to mount a stronger challenge after Raikkonen finished third and Massa fourth in Monaco two weeks ago.

A second practice session will be held later. Training on Saturday will determine grid positions for Sunday's race.

Button commands the standings with 51 points, with Barrichello on 35 points and Vettel on 23. (dpa)