Jorge Lorenzo was quickest at Jerez on Saturday as MotoGP's final pre-season test kicked off amid heavy downpours.
The rain was torrential for long periods, meaning very little track action for much of the day.
Only when conditions eased slightly early in the afternoon did the field take to the circuit in earnest.
Lorenzo managed to set a 1m47.423s on his Yamaha, putting him one second clear of Honda duo Dani Pedrosa and Marc Marquez.
Ducati had a happier time in the wet than it has in the dry of late, filling the final top five spots with Pramac's Andrea Iannone and factory test rider Michele Pirro.
Valentino Rossi was back in sixth on the second Yamaha.
Paul Bird rider Yonny Hernandez led the CRT pack in 12th overall.
Testing continues through Sunday and Monday.
Pos Rider Team/Bike Time Gap 1. Jorge Lorenzo Yamaha 1m47.423s 2. Dani Pedrosa Honda 1m48.474s + 1.051s 3. Marc Marquez Honda 1m48.524s + 1.101s 4. Andrea Iannone Pramac Ducati 1m48.984s + 1.561s 5. Michele Pirro Ducati 1m49.292s + 1.869s 6. Valentino Rossi Yamaha 1m49.443s + 2.020s 7. Nicky Hayden Ducati 1m49.643s + 2.220s 8. Cal Crutchlow Tech 3 Yamaha 1m49.692s + 2.269s 9. Stefan Bradl LCR Honda 1m49.790s + 2.367s 10. Andrea Dovizioso Ducati 1m50.266s + 2.843s 11. Ben Spies Pramac Ducati 1m50.957s + 3.534s 12. Yonny Hernandez PBM Aprilia 1m51.269s + 3.846s 13. Alvaro Bautista Gresini Honda 1m51.277s + 3.854s 14. Karel Abraham Cardion Aprilia 1m51.333s + 3.910s 15. Claudio Corti Forward FTR-Kawasaki 1m52.034s + 4.611s 16. Bradley Smith Tech 3 Yamaha 1m52.047s + 4.624s 17. Danilo Petrucci Ioda Suter-BMW 1m52.180s + 4.757s 18. Hector Barbera Avintia FTR-Kawasaki 1m52.291s + 4.868s 19. Hiroshi Aoyama Avintia FTR-Kawasaki 1m52.676s + 5.253s 20. Colin Edwards Forward FTR-Kawasaki 1m53.992s + 6.569s 21. Bryan Staring Gresini FTR-Honda 1m56.119s + 8.696s 22. Michael Laverty PBM-Aprilia 1m59.470s + 12.047s 23. Lukas Pesek Ioda Suter-BMW 2m00.093s + 12.670s