Red Bull’s Sebastian Vettel led the timesheets Friday in the second practice session of the Korean Grand Prix, where he hopes to close the four-point gap on championship leader Fernando Alonso.
Vettel's teammate Mark Webber was just three-hundredths behind while Alonso was a further three-tenths back in his Ferrari.
“All in all we can be quite happy but I think it looks extremely tight," the reigning champions told Red Bull's site.
"I’m not happy with every run we had today, but I think the track was changing quite a lot this morning, it was better than we expected. I think we have to improve ourselves to match the others.”
Lewis Hamilton, who went fastest in first practice earlier Friday, could only manage eighth later.
"The first session was fantastic. I don't really know what's happened in this session," the 2008 champion said.
Marussia’s drivers Charles Pic will lose 10 grid positions due to a illegal engine change.
Teams are allowed eight engines per season and Pic was using his ninth.