Romain Grosjean thrust Lotus to the top of the times with a late charge in opening practice for the Abu Dhabi Grand Prix.
Amid all the focus on his team-mate Kimi Raikkonen's relationship with the squad, Grosjean bucked the usual Friday morning trend by waiting until the closing moments to set his best time.
Grosjean's 1m44.241s lap put him 0.192 seconds clear of Lewis Hamilton, who would normally have expected to stay up front after winning the traditional mid-session dice for top spot.
No one set a flying lap for the first half hour, and it was near the hour mark before the Mercedes and Red Bulls really raised the bar.
Hamilton emerged on top for Mercedes at that stage, 0.066s ahead of Sebastian Vettel's Red Bull.
The world champion had a slight scare at the end of the session, when he misjudged his entry to the Red Bull pit stall and required some evasive action from his crew as he locked up.
Vettel's team-mate Mark Webber beat Nico Rosberg's Mercedes to fifth, with the in-the-spotlight Raikkonen seventh.
Paul di Resta put Force India in an encouraging seventh place. His team-mate Adrian Sutil moved aside for James Calado this time. The GP2 title contender was 14th.
Other 'Friday drivers' in action were Caterham's Heikki Kovalainen and Marussia's Rodolfo Gonzalez, who were 20th and 22nd.
The McLarens ended up eighth and 10th, split by the Williams of Pastor Maldonado.
Ferrari had a low-key start, with Fernando Alonso and Felipe Massa 12th and 17th.
Pos Driver Team Time Gap Laps 1. Romain Grosjean Lotus-Renault 1m44.241s 20 2. Lewis Hamilton Mercedes 1m44.433s +0.192s 22 3. Sebastian Vettel Red Bull-Renault 1m44.499s +0.258s 18 4. Mark Webber Red Bull-Renault 1m44.712s +0.471s 18 5. Nico Rosberg Mercedes 1m44.741s +0.500s 23 6. Kimi Raikkonen Lotus-Renault 1m44.929s +0.688s 21 7. Paul di Resta Force India-Mercedes 1m45.040s +0.799s 19 8. Jenson Button McLaren-Mercedes 1m45.099s +0.858s 19 9. Pastor Maldonado Williams-Renault 1m45.150s +0.909s 23 10. Sergio Perez McLaren-Mercedes 1m45.331s +1.090s 19 11. Nico Hulkenberg Sauber-Ferrari 1m45.378s +1.137s 21 12. Fernando Alonso Ferrari 1m45.440s +1.199s 17 13. Valtteri Bottas Williams-Renault 1m45.823s +1.582s 21 14. James Calado Force India-Mercedes 1m45.924s +1.683s 19 15. Esteban Gutierrez Sauber-Ferrari 1m46.068s +1.827s 17 16. Jean-Eric Vergne Toro Rosso-Ferrari 1m46.114s +1.873s 21 17. Felipe Massa Ferrari 1m46.124s +1.883s 17 18. Daniel Ricciardo Toro Rosso-Ferrari 1m46.126s +1.885s 20 19. Charles Pic Caterham-Renault 1m47.600s +3.359s 21 20. Heikki Kovalainen Caterham-Renault 1m47.670s +3.429s 21 21. Jules Bianchi Marussia-Cosworth 1m47.723s +3.482s 22 22. Rodolfo Gonzalez Marussia-Cosworth 1m49.565s +5.324s 21