McLaren's Heikki Kovalainen was fastest in practice for Formula One's Turkish Grand Prix.
The Finnish driver set a fastest lap today of 1 minute, 28.841 seconds across both practice sessions to edge Renault's Fernando Alonso by 0.006 seconds.
Williams driver Nico Rosberg was the only other driver to finish under the 1:29 mark, while BMW Sauber's Robert Kubica and Kazuki Nakajima of Williams rounded out the top-five.
Championship leader Jenson Button of Brawn GP had a best lap of 1:29.430 - more than half a second off Kovalainen's pace.
Button has won five of the season's first six races to lead the overall standings with 51 points. Teammate Rubens Barrichello, who was slightly faster than Button, is second with 35 points followed by Red Bull's Sebastian Vettel - the season's only other race winner - on 23.
Vettel experienced mechanical difficulties with an hour to run in the second practice session as his car was removed from the track.
Ferrari and Red Bull are expected to offer Brawn GP the toughest opposition for Sunday's 58-lap race at the Istanbul Park Circuit, where Felipe Massa is looking to win for the fourth straight year.
The Ferrari driver managed a best lap of 1:29.416 in warm conditions.
Teams arrived at Istanbul with a variety of aerodynamic upgrades for the high-speed track, which offered a significant change to the narrow street course at the preceding Monaco GP.
Lewis Hamilton, who was nearly six-tenths off his teammate's pace, was one of several drivers to spin, as the defending F1 champion twice lost control of his car during the second session.
Nakajima and one of the Force India cars also tangled, although neither car was damaged.