Mercedes driver Lewis Hamilton got the better of runaway Formula One leader Sebastian Vettel by setting the fastest time in Friday's practice for the Korean Grand Prix.
Saturday's qualifying shapes again as being a shootout between Mercedes and Red Bull, with Hamilton's teammate, Nico Rosberg, and the Red Bulls of Vettel and Mark Webber all within two-tenths of a second of the leading time.
Red Bull and Mercedes have between them taken every front-row grid spot for the past 10 races.
"It's the first time I can remember that second practice has really gone well for me," Hamilton said. "We haven't changed anything but the day just went smoothly and all the processes with the team worked well. I love this track."
Vettel was less enthusiastic about the day's work and acknowledged Mercedes looms as a threat to his ambitions for a third straight pole.
"There is some room for improvement," Vettel said. "It will be close with Mercedes; of course we're not sure what others were doing with their fuel loads, but it seems close ahead of tomorrow's qualifying."
Vettel has won the past three races, the previous two in Korea, and is zooming toward a fourth successive world title.
Ferrari's Fernando Alonso, who is in second place in the drivers' standings — a fading 60 points behind Vettel — was only seventh fastest, seven-tenths of a second off Hamilton's time, but all season the Italian team has been able to overcome short-run speed deficits and produce a better package on race day.
In the morning session, several drivers ran wide off the unrubbered and dusty surface. Notably, Lotus' Kimi Raikkonen impacted side on with the tire barriers just as the session ended.
The Finn admitted it was his error as he lost control of the car's rear end, but allayed any fears that it damaged his injured back and declared himself ready to participate in Saturday qualifying.
There was less slipping and sliding in the afternoon session, and Hamilton was able to wipe a second off his best lap from the morning, which also topped that session.
Ferrari and Lotus split the next four places behind the top two teams: Ferrari's Felipe Massa was fifth fastest and Alonso seventh, with Lotus' Romain Grosjean sixth and Raikkonen eighth. McLaren's Jenson Button was ninth, and Force India's Adrian Sutil 10th.
Webber is unlikely to be a factor in qualifying, as he carries a penalty into the race that will see him fall 10 grid places on his qualifying position, so the team is expected to use an alternative strategy.
Mercedes has outperformed Red Bull in the overall pole showdown this season, having taken top spot in eight of 13 races, with Vettel getting the other five.
Pirelli chief Paul Hembery said he anticipated a two-stop strategy in the race from most teams, with the super-soft tires having a life of around 15 laps and the mediums around 25, with a one second per lap speed differential between them.