Championship leader Mark Webber led a trio of Formula One title rivals at the top of the practice timesheets after a slippery first day at South Korea's new circuit on Friday.
The Australian spun his Red Bull off at turn 12 before returning to the track and immediately setting the fastest lap of the day, one minute 37.942 seconds, in the afternoon session.
Ferrari's Fernando Alonso, second in the championship with Red Bull's Sebastian Vettel and 14 points adrift, was 0.190 slower after lapping only 15th fastest in the first session on a dusty surface.
McLaren's Lewis Hamilton, fourth in the title battle and 28 points behind Webber, was third fastest after setting the pace before lunch with a best lap of one minute 40.887 seconds.
In a measure of how competitive the field is, four teams filled the top four places with Poland's Robert Kubica fourth in second practice for Renault.
Vettel was seventh, the position Webber occupied in the morning.
McLaren's Jenson Button, the reigning champion, mirrored his overall championship position by ending both sessions in fifth place.
The Briton's car had to be doused with fire extinguishers during the second session as the rear overheated but there was no significant damage and he was able to get back on track.
A decent turnout of fans, many of them schoolchildren getting their first taste of Formula One, watched as drivers struggled to stay on a dusty track that has yet to witness any actual racing.
Hamilton only ventured out late in the morning, but it was not long before he lit up the timing screens with the fastest times through all three sectors.
Vettel then delivered a late quick lap with faster times through the more twisty second and third sectors.
The struggling Hispania team suffered setbacks in both sessions, with Brazilian Bruno Senna careering off the track with an apparent rear suspension failure in the morning and Sakon Yamamoto hitting the wall and stalling in the later stint.
Drivers sent up regular puffs of dirt as they carved through the final corner of an anti-clockwise circuit that had resembled a building site only days earlier.
Although grip levels improved throughout the morning, conditions were treacherous with the pit lane giving particular cause for concern.
Mercedes chief strategist James Vowles told the BBC that they were treating the track like "a living entity".
"Every time the drivers go out the track will feel different. The pit lane is very dirty and we are a little bit concerned. In eight years of doing this, it is the worst I have seen," he added.
Finland's Heikki Kovalainen, for Lotus, had the honour of being the first Formula One driver to venture out on the hastily-completed track, which had its final layer of asphalt laid down only two weeks ago.