Red Bull took charge in the second Friday practice session for the Korean Grand Prix, as Sebastian Vettel edged out team-mate Mark Webber by just 0.032 seconds.
Although the Red Bulls were relatively quiet in first practice, they scrapped over the top spot for almost the entirety of practice two.
Michael Schumacher and Felipe Massa briefly intruded early on, but after Webber went fastest on a 1m39.404s just before the half-hour mark, Red Bull was never headed.
Its drivers kept exchanging positions, though.
Vettel beat Webber's benchmark by 0.3s after 34 minutes, and stayed in front until they both moved onto super softs with nearly an hour gone.
Webber initially had the edge, taking first place back with a 1m38.864s.
Vettel had made mistakes and locked up on his first super-soft laps, but he then pulled everything together and set a 1m38.832s to secure Friday honours.
Alonso ended up Red Bull's closest challenger in third, ahead of Jenson Button's McLaren and Schumacher's Mercedes.
Lewis Hamilton was only eighth in the second McLaren, suffering a major lock-up into Turn 1 on one of his final outings.
In a generally quiet session, other incidents included Sergio Perez's day ending early with an acctuator glitch on his Sauber, and Bruno Senna spinning his Williams.
Pos Driver Car Time Gap Laps 1. Sebastian Vettel Red Bull-Renault 1m38.832s 33
2. Mark Webber Red Bull-Renault 1m38.864s + 0.032 33
3. Fernando Alonso Ferrari 1m39.160s + 0.328 28
4. Jenson Button McLaren-Mercedes 1m39.219s + 0.387 29
5. Michael Schumacher Mercedes 1m39.330s + 0.498 31
6. Felipe Massa Ferrari 1m39.422s + 0.590 30
7. Nico Rosberg Mercedes 1m39.584s + 0.752 36
8. Lewis Hamilton McLaren-Mercedes 1m39.717s + 0.885 25
9. Nico Hulkenberg Force India-Mercedes 1m39.739s + 0.907 33
10. Kimi Raikkonen Lotus-Renault 1m39.839s + 1.007 26
11. Romain Grosjean Lotus-Renault 1m39.957s + 1.125 28
12. Bruno Senna Williams-Renault 1m40.089s + 1.257 32
13. Paul di Resta Force India-Mercedes 1m40.112s + 1.280 34
14. Kamui Kobayashi Sauber-Ferrari 1m40.445s + 1.613 28
15. Sergio Perez Sauber-Ferrari 1m40.745s + 1.913 11
16. Jean-Eric Vergne Toro Rosso-Ferrari 1m40.789s + 1.957 31
17. Daniel Ricciardo Toro Rosso-Ferrari 1m40.997s + 2.165 32
18. Pastor Maldonado Williams-Renault 1m41.200s + 2.368 33
19. Heikki Kovalainen Caterham-Renault 1m41.602s + 2.770 23
20. Timo Glock Marussia-Cosworth 1m42.596s + 3.764 28
21. Charles Pic Marussia-Cosworth 1m43.066s + 4.234 21
22. Vitaly Petrov Caterham-Renault 1m43.067s + 4.235 22
23. Narain Karthikeyan HRT-Cosworth 1m43.869s + 5.037 36
24. Pedro de la Rosa HRT-Cosworth 1m44.533s + 5.701 24
All timing unofficial