Sebastian Vettel signalled his menacing intent to oust Fernando Alonso at the top of the championship table, driving the fastest lap in practice at the Korean Grand Prix on Friday.
The Red Bull driver is four points behind the Ferrari going into Sunday's race, after which there are just four grand prix left in what has been a highly unpredictable season.
Vettel, the man in form after imperious back-to-back victories in Singapore and then Japan last week, clocked a time of one minute 38.832 seconds in the second session, 0.032 seconds ahead of fellow Red Bull driver Mark Webber.
The Spaniard Alonso, desperate to get back among the points after retiring in Suzuka, registered the third-fastest time, 0.328 seconds slower than his title rival Vettel.
The McLaren of Jenson Button was fourth fastest, next up was the Mercedes of Michael Schumacher, Felipe Massa in a Ferrari and Schumacher's team-mate Nico Rosberg.
Briton Lewis Hamilton, quickest in the first session at a cool but sunny Yeongam, could only clock the eighth-fastest time in the afternoon.
"All in all we can be quite happy, but I think it looks extremely tight," said Vettel, the double reigning world champion.
"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.
"This afternoon it was quite slippery to start with, but then I think it got a little bit better, so all in all the car felt alright and now we see what we can do for tomorrow. I think we have to improve ourselves to match the others."
Alonso, who did not finish in Suzuka because of a puncture moments after the start, said: "It's hard to know where we are compared to the others because today we focused mainly on ourselves, working this morning on a comparison of various ideas relating to car configuration and in the afternoon on tyres."
A disconsolate Hamilton, who needs victory at the weekend to stay in the hunt for the world title, said: "I was struggling a bit with the set-up today.
"The Red Bulls seem pretty quick, but we will keep pushing and obviously Jenson was not that far off the pace today. So if we can get the set-up right and everything, maybe we will be competitive.
"The first session was great, I don't know really what happened in the second."