Jenson Button proved that McLaren's Friday pace was not down to the weather as he went quickest in the final practice session for the Korean Grand Prix at Yeongam.
Button initially hit the front with 23 minutes of the hour-long session to go in a time of 1m38.005s, but was knocked off the top spot by his teammate Lewis Hamilton shortly afterward.
Hamilton looked as though the fastest time would be his as he improved his pace to 1m37.199s with five minutes to go on super-soft tires. But a later attempt to go even quicker was spoiled when he came across the slower Mercedes of Michael Schumacher at the twisty final section of the lap.
Free from traffic, Button then grabbed the top spot on his final lap of the session in 1m36.910s, a time 0.289s quicker than Hamilton's.
Mark Webber was Red Bull's top representative in third, ahead of the Ferraris of Fernando Alonso and Felipe Massa and Schumacher's Mercedes.
Vitaly Petrov was seventh for Renault with Adrian Sutil - very quick in the wet on Friday - next up in his Force India.
World champion Sebastian Vettel was only ninth, the German having flat-spotted a right-front supersoft tyre during a long run midway through the session.
He did have one final attempt on a fresh set of Pirellis, but was baulked on successive laps by Jaime Alguersuari's Toro Rosso, having set the fastest first sector of all on the first of his attempts.
Nico Rosberg completed the top 10 for Mercedes, ahead of Alguersuari and Sebastien Buemi.
Bruno Senna wound up 16th after spinning his Renault at the exit of Turn 13 and breaking his front wing against the wall, while Jarno Trulli understeered off at Turn 14 a minute earlier after locking-up his front-right tyre.
Daniel Ricciardo was another to lose a significant amount of track time, the HRT driver suffering a water leak on his car.
Pos Driver Team Time Laps
1. Jenson Button McLaren-Mercedes 1m36.910s 18
2. Lewis Hamilton McLaren-Mercedes 1m37.199s + 0.289 18
3. Mark Webber Red Bull-Renault 1m37.723s + 0.813 23
4. Fernando Alonso Ferrari 1m38.029s + 1.119 21
5. Felipe Massa Ferrari 1m38.434s + 1.524 18
6. Michael Schumacher Mercedes 1m39.559s + 2.649 23
7. Vitaly Petrov Renault 1m39.612s + 2.702 20
8. Adrian Sutil Force India-Mercedes 1m39.660s + 2.750 22
9. Sebastian Vettel Red Bull-Renault 1m39.695s + 2.785 22
10. Nico Rosberg Mercedes 1m39.743s + 2.833 25
11. Paul di Resta Force India-Mercedes 1m39.847s + 2.937 22
12. Jaime Alguersuari Toro Rosso-Ferrari 1m39.851s + 2.941 20
13. Sebastien Buemi Toro Rosso-Ferrari 1m39.964s + 3.054 21
14. Kamui Kobayashi Sauber-Ferrari 1m40.005s + 3.095 17
15. Sergio Perez Sauber-Ferrari 1m40.030s + 3.120 18
16. Bruno Senna Renault 1m40.451s + 3.541 28
17. Pastor Maldonado Williams-Cosworth 1m40.529s + 3.619 20
18. Rubens Barrichello Williams-Cosworth 1m40.711s + 3.801 22
19. Heikki Kovalainen Lotus-Renault 1m41.909s + 4.999 18
20. Jarno Trulli Lotus-Renault 1m41.945s + 5.035 13
21. Timo Glock Virgin-Cosworth 1m43.275s + 6.365 19
22. Jerome D'Ambrosio Virgin-Cosworth 1m44.377s + 7.467 16
23. Vitantonio Liuzzi HRT-Cosworth 1m44.421s + 7.511 22
24. Daniel Ricciardo HRT-Cosworth 1m45.958s + 8.233 11
All Timing Unofficial