Red Bulls Vettel was already flying high in Friday's practice sessions but he confirmed his superiority by leading the final practice session with a time of one minute 37.642 seconds.
McLaren managed to recover from their poor showing during the second practice session, with Lewis Hamilton and Jenson Button posting the second and third best timings, although Hamilton was still way off Vettel's timing of one minute 38.169 seconds, with Button adrift by another 0.3 seconds.
The McLaren drivers were followed by Lotus' Romain Grosjean and Kimi Raikkonen in fourth and fifth respectively, while current Championship leader Fernando Alonso of Ferrari, desperately trying to hang on to a four point lead over Vettel, was sixth with a one minute 38.705 seconds.
A look at the Yeongam Circuit
Esteemed Formula 1 commentator Steve Slater previews the action.
Unlike his Red Bull teammate, Mark Webber struggled in the final practice and ended up seventh after failing to get out for a run on the super-soft tyres as his mechanics worked on the engine of his RB8.
The top 10 was rounded off by Felipe Massa [8th], Pastor Maldonado [9th] and Nico Hulkenberg [10th].
Sergio Perez was 11th but could find himself in trouble with the stewards for blocking Narain Karthikeyan, while Mercedes' Nico Rosberg and Michael Schumacher were 12th and 13th respectively.
They were followed by Force India's Paul Di Resta [14th] and Sauber's Kamui Kobayashi [15th].
Despite Vettel's incredible lap, there was comfort for his rivals during the longer runs on the soft tyre early in the session.
While the German was quickest on the harder of the two Pirelli compounds in use this weekend, Hamilton, Button and Alonso all looked stronger in terms of race pace.
Here are some of the major stories leading up to Saturday's Japanese Grand Prix qualifying:
Lewis Hamilton is feeling dejected with his title hopes looking increasingly slim after a difficult day in Korea.
Jenson Button is fully focused on securing the constructors' championship for McLaren with his individual hopes of glory all but over.
Michael Schumacher suffered the ignominy of being reprimanded by the stewards for impeding the two HRTs during second practice for the Korean Grand Prix.
Kimi Raikkonen insists he does not care about his lack of pace in Korean Grand Prix practice and expects Lotus to take a big step forward as the weekend progresses.
Ferrari team manager Massimo Rivola is confident the team will be "very, very competitive" in Korea as they look to fight back in the race for the title.
Kamui Kobayashi admits he is disillusioned with the current trend of drivers securing Formula One seats through their sponsorship links.
Sebastian Vettel and Fernando Alonso are refusing to write off Lewis Hamilton's chances of snatching the world title from their respective grasps.
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