Jenson Button topped the timesheets in final practice in what proved to be a battle of the two McLarens.
Getting some dry running for the first time this weekend, Button and Lewis Hamilton proved to be in a class of their own as they lapped the 5.615km Yeongam circuit.
Button crossed the line with a 1:36.910 as the chequered flag fell to to take the P1 slot off Hamilton by 0.289s.
Mark Webber was third ahead of the two Ferraris of Fernando Alonso and Felipe Massa.
However, it must be noted that Sebastian Vettel did have the pace on the softer option tyres, he just also had the traffic of Jaime Alguersuari and was not able to put in a clean lap without catching - and being slowed - by the Toro Rosso driver.
Report: Track temperature was up to 29'C as Practice Three got underway under cloudy skies and with a damp spot at the end of pit lane. Bruno Senna was the first out while Nico Rosberg posted the first time, a 1:41.389 for the Merc GP driver.
Mark Webber was the next to lead the way, followed by Michael Schumacher and then Sebastian Vettel, who clocked a 1:39.799 inth early running. Lewis Hamilton overhauled Vettel at the front, posting fastest times in all three sectors on his way to a 1:38.210.
Bruno Senna, meanwhile, hit a wet kerb, put his Renault into a spin, and clipped the wall at Turn 14 with the nose of his car. The Brazilian kept it run, through a 180' and headed back to the pits. HRT's Daniel Ricciardo stalled in pit lane and needed a helping hand from his mechanics.
Halfway through final practice Felipe Massa was but was a full second off Hamilton's time while Jenson Button, who is using a new chassis - number 01, was third ahead of Schumacher, Fernando Alonso, Rosberg, Vettel and Jaime Alguersuari.
Button ventured out again, improving to second and closing the gap to Hamilton to a tenth. However, the 2008 Champ responded with another run of fastest sector times and increased it to 0.295. Alonso took third off Massa.
Button finally put together the lap that overhauled his team-mate, jumping ahead by 0.015s. Hamilton responded again, moving 0.410s clear of Button. Alonso, who was third, pitted only to be surrounded by a sea of Ferrari personnel blocking the media from getting a good look at his new front wing.
With ten minutes remaining, most switched to the softer option tyres with Button closing the gap to Hamilton only for the latter to once again extend it. Webber went from 14th to third, Vettel from 10th to nowhere as he came up behind Jaime Alguersuari, next lap was more of the same with Vettel finally passing Alguersuari at the very end of it to take ninth.
Button put in a late charge to take the P1 slot off Hamilton with Webber finishing in third place.
01. Jenson Button McLaren-Mercedes 1m36.910 18 laps
02. Lewis Hamilton McLaren-Mercedes 1m37.199 + 0.289 18 laps
03. Mark Webber Red Bull-Renault 1m37.723 + 0.813 23 laps
04. Fernando Alonso Ferrari 1m38.029 + 1.119 21 laps
05. Felipe Massa Ferrari 1m38.434 + 1.524 18 laps
06. Michael Schumacher Mercedes 1m39.559 + 2.649 23 laps
07. Vitaly Petrov Renault 1m39.612 + 2.702 20 laps
08. Adrian Sutil Force India-Mercedes 1m39.660 + 2.750 22 laps
09. Sebastian Vettel Red Bull-Renault 1m39.695 + 2.785 22 laps
10. Nico Rosberg Mercedes 1m39.743 + 2.833 25 laps
11. Paul di Resta Force India-Mercedes 1m39.847 + 2.937 22 laps
12. Jaime Alguersuari Toro Rosso-Ferrari 1m39.851 + 2.941 20 laps
13. Sebastien Buemi Toro Rosso-Ferrari 1m39.964 + 3.054 21 laps
14. Kamui Kobayashi Sauber-Ferrari 1m40.005 + 3.095 17 laps
15. Sergio Perez Sauber-Ferrari 1m40.030 + 3.120 18 laps
16. Bruno Senna Renault 1m40.451 + 3.541 28 laps
17. Pastor Maldonado Williams-Cosworth 1m40.529 + 3.619 20 laps
18. Rubens Barrichello Williams-Cosworth 1m40.711 + 3.801 22 laps
19. Heikki Kovalainen Lotus-Renault 1m41.909 + 4.999 18 laps
20. Jarno Trulli Lotus-Renault 1m41.945 + 5.035 13 laps
21. Timo Glock Virgin-Cosworth 1m43.275 + 6.365 19 laps
22. Jerome D'Ambrosio Virgin-Cosworth 1m44.377 + 7.467 16 laps
23. Vitantonio Liuzzi HRT-Cosworth 1m44.421 + 7.511 22 laps
24. Daniel Ricciardo HRT-Cosworth 1m45.958 + 8.233 11 laps