McLaren pair Juan Pablo Montoya and Kimi Raikkonen took little time getting to grips with the new Istanbul circuit in practice for the Turkish Grand Prix.
Toyota tester Ricardo Zonta set the best time of one minute 25.583 seconds, with McLaren's Pedro de la Rosa second.
But Raikkonen and Montoya took it in turns to go fastest of the race drivers in Friday's two one-hour sessions.
BAR's Jenson Button was next quickest ahead of Red Bull's Vitantonio Liuzzi and Renault's Fernando Alonso.
Championship leader Alonso's team-mate Giancarlo Fisichella was eighth, with David Coulthard 12th for Red Bull and world champion Michael Schumacher 13th in the Ferrari.
The new 5.3km Istanbul Otodrom is one of only three circuits on the Formula One calendar which run anticlockwise.
The drivers' previous experience of it had been on computer simulators and video games, and De la Rosa was the first out as the teams began work on their set-ups for Sunday's race.
By the end of the session, all 25 drivers had completed a timed run as the need to learn the track took priority above the desire to conserve their engines.
De la Rosa's lap of 1:27.882 put him 0.571 seconds ahead of Raikkonen, who won the last race in Hungary.
Several drivers made mistakes, with Schumacher spinning his Ferrari across the gravel at turn 12 late in the session.
Mark Webber also took to the gravel in his Williams after running wide, Liuzzi lost control at turn eight, Nick Heidfeld's Williams went off at turn one and Rubens Barrichello spun his Ferrari at turn three.
Montoya went quicker than Raikkonen in the second session, the Colombian's lap of 1:26.525 almost a second slower than the benchmark set by Zonta with his final lap of the day.
Friday practice times:
1 Ricardo Zonta (Br) Toyota one minute 25.583 seconds
2 Pedro de la Rosa (Sp) McLaren-Mercedes 1:26.196
3 Juan Pablo Montoya (Col) McLaren-Mercedes 1:26.525
4 Kimi Raikkonen (Fin) McLaren-Mercedes 1:27.274
5 Jenson Button (GB) BAR-Honda 1:27.346
6 Vitantonio Liuzzi (It) Red Bull-Cosworth 1:27.578
7 Fernando Alonso (Sp) Renault, 25, 1:27.579
8 Giancarlo Fisichella (It) Renault, 29, 1:27.673
9 Jarno Trulli (It) Toyota 1:27.964
10 Takuma Sato (Jpn) BAR-Honda 1:28.081
11 Mark Webber (Aus) Williams-BMW 1:28.120
12 David Coulthard (Sco) Red Bull-Cosworth 1:28.235
13 Michael Schumacher (Ger) Ferrari 1:28.293
14 Jacques Villeneuve (Can) Sauber-Petonas 1:28.404
15 Rubens Barrichello (Br) Ferrari 1:28.460
16 Ralf Schumacher (Ger) Toyota 1:28.641
17 Felipe Massa (Br) Sauber-Petronas 1:28.681
18 Christian Klien (Aut) Red Bull-Cosworth 1:28.828
19 Nick Heidfeld (Ger) Williams-BMW 1:28.959
20 Tiago Monteiro (Por) Jordan-Toyota 1:30.626
21 Robert Doornbos (Mon) Jordan-Toyota 1:30.628
22 Christijan Albers (Neth) Minardi-Cosworth 1:30.730
23 Nicolas Kiesa (Den) Jordan-Toyota 1:30.884
24 Narain Karthikeyan (Ind) Jordan-Toyota 1:30.899
25 Enrico Toccacelo (It) Minardi 1:32.813