Jorge Lorenzo denied Valentino Rossi a home top spot in Mugello practice, as Marc Marquez escaped a violent accident.
Marquez, who had been fastest in the morning, lost control under braking at the end of a 200mph straight. His Honda slid onto the wet grass lining the track and slammed to the ground before sliding into the gravel. Marquez crawled away from the wreckage and was taken straight to the medical center. Initial notification from race control was that the Spaniard had not sustained any serious injuries.
The accident was the worse part of a difficult session for Honda, which could only watch as rival Yamaha dominated.
Rossi and Lorenzo swapped first position relentlessly, in one of seven-time Mugello MotoGP race winner Rossi's strongest performances since rejoining Yamaha.
The home crowd will have to wait to see Rossi end a session on top, though, as Lorenzo snatched the place away in the closing moments with a 1m48.375s, 0.034 second faster than the sister M1. Yamaha filled the top three positions, with Cal Crutchlow third for Tech 3.
In addition to Marquez's accident, Crutchlow's team-mate Bradley Smith also needed a trip to the medical centre following a violent crash. He is being assessed for a possible left arm injury.
Ducati had an encouraging session on home ground. Nicky Hayden was fourth, pushing championship leader Dani Pedrosa's Honda back to fifth.
Hayden's team-mates Andrea Dovizioso and Michele Pirro were seventh and 10th, but second-best Ducati was Pramac's Andrea Iannone, who benefited from tailing Rossi on his way to sixth.
Aspar rider Randy de Puniet led the CRT pack in ninth place.
Pos Rider Team/Bike Time Gap
1. Jorge Lorenzo Yamaha 1m48.375s
2. Valentino Rossi Yamaha 1m48.409s + 0.034s
3. Cal Crutchlow Tech 3 Yamaha 1m48.672s + 0.297s
4. Nicky Hayden Ducati 1m49.377s + 1.002s
5. Dani Pedrosa Honda 1m49.383s + 1.008s
6. Andrea Iannone Pramac Ducati 1m49.467s + 1.092s
7. Andrea Dovizioso Ducati 1m49.543s + 1.168s
8. Stefan Bradl LCR Honda 1m49.595s + 1.220s
9. Randy de Puniet Aspar Aprilia 1m49.599s + 1.224s
10. Michele Pirro Ducati 1m49.649s + 1.274s
11. Alvaro Bautista Gresini Honda 1m49.733s + 1.358s
12. Aleix Espargaro Aspar Aprilia 1m49.769s + 1.394s
13. Bradley Smith Tech 3 Yamaha 1m50.103s + 1.728s
14. Marc Marquez Honda 1m50.210s + 1.835s
15. Hector Barbera Avintia FTR-Kawasaki 1m50.400s + 2.025s
16. Ben Spies Pramac Ducati 1m51.105s + 2.730s
17. Colin Edwards Forward FTR-Kawasaki 1m51.433s + 3.058s
18. Karel Abraham Cardion Aprilia 1m51.528s + 3.153s
19. Yonny Hernandez PBM Aprilia 1m51.644s + 3.269s
20. Danilo Petrucci Ioda-Suter-BMW 1m51.937s + 3.562s
21. Hiroshi Aoyama Avintia FTR-Kawasaki 1m52.182s + 3.807s
22. Claudio Corti Forward FTR-Kawasaki 1m53.314s + 4.939s
23. Michael Laverty PBM-Aprilia 1m53.480s + 5.105s
24. Bryan Staring Gresini FTR-Honda 1m54.231s + 5.856s
25. Lukas Pesek Ioda-Suter-BMW 1m54.829s + 6.454s