Sebastian Vettel proved to be the driver to beat in Korea on Friday as he edged team-mate Mark Webber by 0.032s in Practice Two.
Vettel, who moved to within four points of the Championship lead when he claimed his third win of the season last time out in Japan, posted a 1:38.832 on Friday afternoon.
That put the German a mere 0.032s up on Webber while Vettel's main rival and Championship leader Fernando Alonso was third. However, he was three-tenths off the pace.
Practice Two got underway in near perfect conditions with the track temperature up to 30'C as Lewis Hamilton posted the afternoon's first lap time, a 1:41.841.
This sparked a run from his rivals with Kimi Raikkonen, Nico Rosberg, Jenson Button, Michael Schumacher and Paul di Resta, a 1:40.331, hitting the front one after the other.
Schumacher was the first into the 1:39s but his reign was short-lived as World Champion Sebastian Vettel jumped to the front while his team-mate Mark Webber sandwiched the Mercedes driver.
But while lap times were tumbling lap after lap, drivers were still struggling to keep all four wheels on the asphalt with Schumacher, Felipe Massa, Sergio Perez, Charles Pic, Heikki Kovalainen all testing the track's limits.
Perez's session came to an end just before the halfway stage as the 22-year-old, having complained of DRS issues, stopped on the side of the track with a hydraulic problem.
Halfway through the session the top three were Vettel with a 1:39.089, Webber and Button.
A switch to the supersoft tyres saw the two Red Bulls engage in a private battle for the P1 slot with Webber and Vettel taking hundredths off each other's times.
Button was the first to challenge only to lose out to Alonso, however, neither came close to battling the Red Bulls for supremacy.
With drivers swapping to heavier fuel loads and lapping at about seven second short of their previous bests, Vettel was guaranteed his first P1 finish of the weekend, 0.032s ahead of Webber.
01 Sebastian Vettel Red Bull 1:38.832 33 laps
02 Mark Webber Red Bull 1:38.864 0.032 33 laps
03 Fernando Alonso Ferrari 1:39.160 0.328 28 laps
04 Jenson Button McLaren 1:39.219 0.387 29 laps
05 Michael Schumacher Mercedes 1:39.330 0.498 31 laps
06 Felipe Massa Ferrari 1:39.422 0.590 30 laps
07 Nico Rosberg Mercedes 1:39.584 0.752 35 laps
08 Lewis Hamilton McLaren 1:39.717 0.885 25 laps
09 Nico Hulkenberg Force India 1:39.739 0.907 33 laps
10 Kimi Raikkonen Lotus 1:39.839 1.007 26 laps
11 Romain Grosjean Lotus 1:39.957 1.125 28 laps
12 Bruno Senna Williams 1:40.089 1.257 32 laps
13 Paul di Resta Force India 1:40.112 1.280 34 laps
14 Kamui Kobayashi Sauber 1:40.445 1.613 27 laps
15 Sergio Perez Sauber 1:40.745 1.913 11 laps
16 Jean-Eric Vergne Toro Rosso 1:40.789 1.957 31 laps
17 Daniel Ricciardo Toro Rosso 1:40.997 2.165 32 laps
18 Pastor Maldonado Williams 1:41.200 2.368 33 laps
19 Heikki Kovalainen Caterham 1:41.602 2.770 23 laps
20 Timo Glock Marussia 1:42.596 3.764 28 laps
21 Charles Pic Marussia 1:43.066 4.234 20 laps
22 Vitaly Petrov Caterham 1:43.067 4.235 22 laps
23 Narain Karthikeyan HRT 1:43.869 5.037 36 laps
24 Pedro de la Rosa HRT 1:44.533 5.701 24 laps