Red Bull laid down an ominous marker as they claimed the top two spots in second practice for the Korean Grand Prix.
The Milton Keynes-based team were the dominant force at last weekend's Japanese Grand Prix and they look like again being the pacesetters in Yeongam.
Sebastian Vettel, just four points behind Fernando Alonso in the championship standings, set a time of one minute 38.832 seconds to beat team-mate Mark Webber to top spot by just three-hundredths of a second.
Third place went to Alonso as Ferrari showed signs that updates to the F2012 will make them a more competitive proposition here than in recent races, although he was 0.3 seconds adrift of the Red Bulls.
Jenson Button was fourth in the first of the McLarens while Michael Schumacher was fifth on a track where Mercedes are optimistic of a competitive showing.
Felipe Massa and Nico Rosberg were next up, ahead of Lewis Hamilton in eighth.
Nico Hulkenberg was ninth in the Force India with the Lotus pair of Kimi Raikkonen and Romain Grosjean 10th and 11th.
Bruno Senna was 12th for Williams, with Paul Di Resta 13th ahead of the two Saubers.
The Swiss team secured a podium in Japan with Kamui Kobayashi, but a repeat looks unlikely this weekend as he and team-mate Sergio Perez finished 14th and 15th. The Mexican's frustrations were not helped when he was forced to abandon his car after it ground to a halt halfway through the session.
Pastor Maldonado was a disappointing 18th for Williams, behind the Toro Rossos of Jean-Eric Vergne and Daniel Ricciardo, with the Caterhams, Marussias and HRTs filling out the bottom six places.