MotoGP rookie Marc Marquez headed the second free practice session for the Qatar Grand Prix with a blistering lap late in proceedings at Losail.
The reigning Moto2 champion, who is stepping up to the top class with the factory Honda squad this year, languished down in the lower reaches of the top 10 for most of the session and twice ran wide at Turn 1 early on.
But with just four minutes to go he pumped in a lap of 1m56.477s to knock world champion Jorge Lorenzo off the top spot with the best time of the weekend so far.
Thursday pacesetter Lorenzo's best lap of the session was set on the 2013-spec Yamaha frame that is unlikely to be raced in Qatar, and with a combination of a hard tyre on the front and a soft on the rear.
His Yamaha team-mate Valentino Rossi spent the majority of the session on the top spot, but was knocked back to third by the chequered flag. He used the 2012-spec chassis throughout.
Britain's Cal Crutchlow snuck into fourth at the end of the session on his Tech 3 Yamaha, just ahead of Stefan Bradl's LCR Honda and Andrea Dovizioso on the best of the factory Ducatis.
Marquez's Honda team-mate Dani Pedrosa was the only rider to find the gravel, doing so at Turn 1 in the latter stages of the session. He was seventh.
Ben Spies, who is still recovering from a shoulder injury, and Britain's MotoGP debutant Bradley Smith, both ran wide at Turn 6, but did not crash.
The fastest rider on a CRT bike was Aleix Espargaro, 13th on his Aspar Aprilia.
Under MotoGP's new-for-2013 qualifying regulations, only the overall fastest 10 riders from practices one, two and three combined are certain of making it through to the final part of qualifying, in which pole position will be decided.
Based on combined times, Spies, Smith and Andrea Iannone are set to miss the cut for an automatic Q2 spot as they lie 11th, 12th and 13th. All three have a chance to make it through in FP3 later on Friday.
Pos Rider Team/Bike Time Gap 1. Marc Marquez Honda 1m56.477s 2. Jorge Lorenzo Yamaha 1m56.745s + 0.268s 3. Valentino Rossi Yamaha 1m56.805s + 0.328s 4. Cal Crutchlow Tech 3 Yamaha 1m57.169s + 0.692s 5. Stefan Bradl LCR Honda 1m57.257s + 0.780s 6. Andrea Dovizioso Ducati 1m57.833s + 1.356s 7. Dani Pedrosa Honda 1m57.877s + 1.400s 8. Nicky Hayden Ducati 1m58.040s + 1.563s 9. Ben Spies Pramac Ducati 1m58.137s + 1.660s 10. Alvaro Bautista Gresini Honda 1m58.298s + 1.821s 11. Bradley Smith Tech 3 Yamaha 1m58.340s + 1.863s 12. Andrea Iannone Pramac Ducati 1m58.575s + 2.098s 13. Aleix Espargaro Aspar Aprilia 1m58.631s + 2.154s 14. Yonny Hernandez PBM Aprilia 1m58.871s + 2.394s 15. Hector Barbera Avintia FTR-Kawasaki 1m58.904s + 2.427s 16. Randy de Puniet Aspar Aprilia 1m59.185s + 2.708s 17. Karel Abraham Cardion Aprilia 1m59.809s + 3.332s 18. Danilo Petrucci Ioda-Suter-BMW 2m00.557s + 4.080s 19. Hiroshi Aoyama Avintia FTR-Kawasaki 2m00.652s + 4.175s 20. Lukas Pesek Ioda-Suter-BMW 2m00.919s + 4.442s 21. Colin Edwards Forward FTR-Kawasaki 2m00.940s + 4.463s 22. Claudio Corti Forward FTR-Kawasaki 2m01.321s + 4.844s 23. Bryan Staring Gresini FTR-Honda 2m01.622s + 5.145s 24. Michael Laverty PBM-Aprilia 2m01.816s + 5.339s