Marc Marquez was fastest in a wet second MotoGP practice at Assen, but the big news was that champion Jorge Lorenzo fractured his collarbone in a crash.
Lorenzo was flung over the handlebars of his Yamaha when he went off on standing water at the fast Turn 13.
It was confirmed immediately after the session that he had fractured his left collarbone, putting his participation in the rest of the Dutch Grand Prix weekend in doubt and jeopardizing his championship bid.
As the teams awaited news of Lorenzo's condition, Marquez timed his run in improving conditions to perfection to post a 1m47.617s on his Honda.
Valentino Rossi was the only man to join Marquez in the sub 1m48s bracket, ending the session 0.252 seconds down the road in second.
Rossi's teammate Lorenzo had been running in the top six when he fell, but dropped to 17th at the flag.
In his absence, main title rival Dani Pedrosa wound up third, fractionally ahead of LCR Honda rider Stefan Bradl and the lead Ducati of Andrea Dovizioso.
Nicky Hayden ended one second down on the Italian in sixth, in front of Tech 3 Yamaha's Cal Crutchlow, who had enjoyed spells at the top of the times but was absent in the final minutes when times fell dramatically.
CRT riders locked out the remaining top 10 spots through Danilo Petrucci (Ioda-Suter-BMW) and Paul Bird duo Yonny Hernandez and Michael Laverty.
Aleix Espargaro and Karel Abraham also fell during the 30-minute session, while Marquez suffered an off-track moment but was able to hold onto his works Honda. Espargaro was taken to the medical center for a potential wrist injury to be assessed.
Pos Rider Team/Bike Time Gap
1. Marc Marquez Honda 1m47.617s
2. Valentino Rossi Yamaha 1m47.869s + 0.252s
3. Dani Pedrosa Honda 1m48.240s + 0.623s
4. Stefan Bradl LCR Honda 1m48.594s + 0.977s
5. Andrea Dovizioso Ducati 1m48.682s + 1.065s
6. Nicky Hayden Ducati 1m48.682s + 1.065s
7. Cal Crutchlow Tech 3 Yamaha 1m48.761s + 1.144s
8. Danilo Petrucci Ioda-Suter-BMW 1m49.031s + 1.414s
9. Yonny Hernandez PBM Aprilia 1m49.129s + 1.512s
10. Michael Laverty PBM-Aprilia 1m49.438s + 1.821s
11. Claudio Corti Forward FTR-Kawasaki 1m49.494s + 1.877s
12. Alvaro Bautista Gresini Honda 1m49.646s + 2.029s
13. Michele Pirro Pramac Ducati 1m49.669s + 2.052s
14. Randy de Puniet Aspar Aprilia 1m49.965s + 2.348s
15. Karel Abraham Cardion Aprilia 1m50.418s + 2.801s
16. Aleix Espargaro Aspar Aprilia 1m50.980s + 3.363s
17. Jorge Lorenzo Yamaha 1m51.432s + 3.815s
18. Bradley Smith Tech 3 Yamaha 1m51.908s + 4.291s
19. Andrea Iannone Pramac Ducati 1m52.155s + 4.538s
20. Ivan Silva Avintia FTR-Kawasaki 1m52.347s + 4.730s
21. Lukas Pesek Ioda-Suter-BMW 1m52.485s + 4.868s
22. Hector Barbera Avintia FTR-Kawasaki 1m53.058s + 5.441s
23. Colin Edwards Forward FTR-Kawasaki 1m54.274s + 6.657s
24. Bryan Staring Gresini FTR-Honda 1m55.761s + 8.144s