Rio Haryanto and Caterham team-mate Alexander Rossi locked out the top two spots on the second day of GP2's final pre-season test in Bahrain.
Both men set their fastest times in the morning, with Haryanto just edging proceedings with a 1m39.129s - three tenths of a second quicker than last year's pole time.
Rossi - quickest on the opening day - finished just four hundredths of a second down the road, with both men establishing a comfortable gap to the rest of the pack.
Julian Leal wound up as the pair's closest challenger, just ahead of last year's European Formula 3 champion Raffaele Marciello and DAMS' title-hopeful Jolyon Palmer.
2012 GP3 champion Mitch Evans and McLaren protege Stoffel Vandoorne were the only other drivers able to crack the 1m40s bracket.
Temperatures rose in the afternoon, but with the majority of the field switching focus to long runs the times were significantly slower.
MP Motorsport's Daniel de Jong wound up fastest with a 1m40.508s, followed closely by Johnny Cecotto and Leal.
Pre-season testing concludes on Friday, with the 2014 season opening at the Sakhir track on April 5-6.
Combined times from day two: Pos Driver Team Time Gap Laps 1. Rio Haryanto Caterham 1m39.129s 67 2. Alexander Rossi Caterham 1m39.173s +0.044s 64 3. Julian Leal Carlin 1m39.538s +0.409s 43 4. Raffaele Marciello Racing Engineering 1m39.704s +0.575s 50 5. Jolyon Palmer DAMS 1m39.854s +0.725s 63 6. Mitch Evans Russian Time 1m39.870s +0.741s 42 7. Stoffel Vandoorne ART 1m39.913s +0.784s 78 8. Stephane Richelmi DAMS 1m40.045s +0.916s 53 9. Rene Binder Arden 1m40.126s +0.997s 46 10. Kimiya Sato Campos 1m40.154s +1.025s 58 11. Nathanael Berthon Lazarus 1m40.190s +1.061s 50 12. Artem Markelov Russian Time 1m40.191s +1.062s 44 13. Conor Daly Lazarus 1m40.233s +1.104s 41 14. Adrian Quaife-Hobbs Rapax 1m40.250s +1.121s 67 15. Andre Negrao Arden 1m40.314s +1.185s 48 16. Takuya Izawa ART 1m40.678s +1.549s 76 17. Felipe Nasr Carlin 1m40.786s +1.657s 50 18. Arthur Pic Campos 1m40.840s +1.711s 64 19. Johnny Cecotto Trident 1m40.779s +1.650s 34 20. Vittorio Ghirelli Trident 1m40.991s +1.862s 39 21. Daniel de Jong MP 1m41.041s +1.912s 20 22. Stefano Coletti Racing Engineering 1m41.106s +1.977s 48 23. Jon Lancaster MP 1m41.166s +2.037s 57 24. Simon Trummer Rapax 1m41.436s +2.307s 58 25. Facu Regalia Hilmer 1m41.476s +2.347s 64 26. Daniel Abt Hilmer 1m41.746s +2.617s 40