Sebastian Vettel and Red Bull moved to the front in the final practice session before Korean Grand Prix qualifying.
The champion driver and currently dominant team had been shaded by Mercedes and Lewis Hamilton on Friday.
But with Hamilton not getting a clear run on super-softs at the end of practice three, Vettel led team-mate Mark Webber in a Red Bull one-two.
The duo had been up front for most of the morning, swapping first position in the opening half of the session.
Hamilton eventually pipped them to the quickest time on harder tyres, slipping in a late 1m38.860s.
Drivers then gained anything from half a second to just over a second on super-softs.
Webber started the rush of qualifying simulations with a 1m38.132s, before improving to a 1m38.018s after backing off for a lap.
That was then deposed by Vettel becoming the only man in the 1m37s with a 1m37.881s lap, 0.137 seconds quicker than Webber managed.
Mercedes had to settle for third and fourth this time, with Nico Rosberg ahead of Hamilton, who had traffic early in his super-soft run.
Ferrari and Lotus continued to battle just behind Red Bull and Mercedes. Fernando Alonso was fifth, followed by Romain Grosjean, Felipe Massa and Kimi Raikkonen.
Nico Hulkenberg got Sauber into the top 10 with ninth place in front of Jenson Button's McLaren in a very close upper midfield pack.
Pos Driver Team/Car Time Gap Laps 1. Sebastian Vettel Red Bull-Renault 1m37.881s 17 2. Mark Webber Red Bull-Renault 1m38.018s +0.137s 17 3. Nico Rosberg Mercedes 1m38.318s +0.437s 16 4. Lewis Hamilton Mercedes 1m38.332s +0.451s 15 5. Fernando Alonso Ferrari 1m38.486s +0.605s 13 6. Romain Grosjean Lotus-Renault 1m38.701s +0.820s 19 7. Felipe Massa Ferrari 1m38.816s +0.935s 14 8. Kimi Raikkonen Lotus-Renault 1m38.857s +0.976s 17 9. Nico Hulkenberg Sauber-Ferrari 1m38.961s +1.080s 16 10. Jenson Button McLaren-Mercedes 1m39.114s +1.233s 14 11. Esteban Gutierrez Sauber-Ferrari 1m39.128s +1.247s 15 12. Pastor Maldonado Williams-Renault 1m39.196s +1.315s 16 13. Adrian Sutil Force India-Mercedes 1m39.204s +1.323s 17 14. Sergio Perez McLaren-Mercedes 1m39.274s +1.393s 15 15. Daniel Ricciardo Toro Rosso-Ferrari 1m39.327s +1.446s 17 16. Paul di Resta Force India-Mercedes 1m39.371s +1.490s 19 17. Jean-Eric Vergne Toro Rosso-Ferrari 1m39.665s +1.784s 15 18. Valtteri Bottas Williams-Renault 1m40.128s +2.247s 17 19. Charles Pic Caterham-Renault 1m41.360s +3.479s 19 20. Giedo van der Garde Caterham-Renault 1m41.614s +3.733s 20 21. Jules Bianchi Marussia-Cosworth 1m41.646s +3.765s 14 22. Max Chilton Marussia-Cosworth 1m42.267s +4.386s 17