Jenson Button narrowly beat Nico Rosberg to the fastest time in a dry second practice session at Istanbul Park, while championship leader Sebastian Vettel did not run at all after his morning crash.
The majority of the session was a battle between the McLarens and the Mercedes, with Button and team-mate Lewis Hamilton the early pacesetters, before first Rosberg then Michael Schumacher hit the front towards the end of the first half-hour.
Three-time Istanbul winner Felipe Massa then briefly got Ferrari to the head of the pack with a 1m27.959s lap, 0.3s quicker than Schumacher.
He only stayed in front for three minutes before Rosberg reclaimed the top spot, which he held until just after the hour mark, when Button moved comfortably clear of the pack with a 1m26.456s on the softer tyres.
Rosberg later closed to within 0.065s, but that lap was sufficiently to keep Button in first place to the end.
Hamilton and Schumacher were third and fourth, the latter's car escaping damage in a late spin at Turn 11 which appeared to be triggered when Schumacher was surprised by a Force India coming past him.
Red Bull kept a relatively low profile, with Mark Webber staying in the midfield and doing longer runs for much of the session before eventually doing a time that would stand for fifth, ahead of Massa. Vettel was not able to run at all, the team soon realising that repairing the session one damage in time would be impossible. That means the points leader will go into the rest of the weekend with no dry mileage at all.
Renault's Vitaly Petrov, another man who topped the timing screens fleetingly in the early running, was seventh, while the Force Indias of Paul di Resta and Adrian Sutil sandwiched Sergio Perez's Sauber in the final three top 10 positions.
It was a tough session for Fernando Alonso. A hydraulic problem kept him in the Ferrari garage for a spell, and he later spun at Turn 6 before taking 11th.
The only driver whose mistake took him as far as the barriers was Pastor Maldonado. The Williams driver ran slightly wide on the way out of Turn 8, found a damp patch and slid into the barrier.
At the tail of the field, the Virgins languished some way off even Hispania's pace until the closing stages when both Jerome D'Ambrosio and Timo Glock edged a few tenths ahead of Narain Karthikeyan.
Pos Driver Team Time Laps 1. Jenson Button McLaren-Mercedes 1m26.456s 26 2. Nico Rosberg Mercedes 1m26.521s + 0.065 29 3. Lewis Hamilton McLaren-Mercedes 1m27.033s + 0.577 31 4. Michael Schumacher Mercedes 1m27.063s + 0.607 21 5. Mark Webber Red Bull-Renault 1m27.149s + 0.693 31 6. Felipe Massa Ferrari 1m27.340s + 0.884 37 7. Vitaly Petrov Renault 1m27.517s + 1.061 37 8. Paul di Resta Force India-Mercedes 1m27.725s + 1.269 37 9. Sergio Perez Sauber-Ferrari 1m27.844s + 1.388 32 10. Adrian Sutil Force India-Mercedes 1m28.052s + 1.596 37 11. Fernando Alonso Ferrari 1m28.069s + 1.613 27 12. Sebastien Buemi Toro Rosso-Ferrari 1m28.153s + 1.697 36 13. Nick Heidfeld Renault 1m28.475s + 2.019 35 14. Jaime Alguersuari Toro Rosso-Ferrari 1m28.765s + 2.309 32 15. Pastor Maldonado Williams-Cosworth 1m28.828s + 2.372 19 16. Rubens Barrichello Williams-Cosworth 1m28.946s + 2.490 20 17. Jarno Trulli Lotus-Renault 1m29.409s + 2.953 39 18. Kamui Kobayashi Sauber-Ferrari 1m29.637s + 3.181 27 19. Heikki Kovalainen Lotus-Renault 1m30.281s + 3.825 37 20. Jerome D'Ambrosio Virgin-Cosworth 1m31.035s + 4.579 28 21. Timo Glock Virgin-Cosworth 1m31.221s + 4.765 22 22. Narain Karthikeyan HRT-Cosworth 1m31.320s + 4.864 29 23. Tonio Liuzzi HRT-Cosworth 1m31.989s + 5.533 30 All Timing Unofficial