World championship leader Valentino Rossi leads the timesheets during opening practice for the Dutch MotoGP at Assen.

Rossi and title rival Jorge Lorenzo each have one new Yamaha chassis to try this weekend, while Honda's Marc Marquez has reverted to the 2014 Honda chassis.

Marquez fell on his out-lap, the Spaniard running through the gravel and then sliding off on the grass.

Assen is the only surviving event from the inaugural 1949 grand prix season. Race day is traditionally held on the last Saturday in June, meaning practice starts on a Thursday.

Karel Abraham is absent due to a foot injury at Catalunya...

1. Valentino Rossi ITA Movistar Yamaha MotoGP (YZR-M1) 1m 34.357s [Lap 20/20] 302km/h (Top Speed)2. Marc Marquez ESP Repsol Honda Team (RC213V) 1m 34.552s +0.195s [17/20] 308km/h 3. Dani Pedrosa ESP Repsol Honda Team (RC213V) 1m 34.570s +0.213s [19/19] 309km/h 4. Jorge Lorenzo ESP Movistar Yamaha MotoGP (YZR-M1) 1m 34.772s +0.415s [18/18] 306km/h 5. Pol Espargaro ESP Monster Yamaha Tech 3 (YZR-M1) 1m 34.927s +0.570s [21/21] 307km/h 6. Bradley Smith GBR Monster Yamaha Tech 3 (YZR-M1) 1m 35.042s +0.685s [21/21] 310km/h 7. Maverick Vi?ales ESP Team Suzuki Ecstar (GSX-RR)* 1m 35.050s +0.693s [18/19] 303km/h 8. Aleix Espargaro ESP Team Suzuki Ecstar (GSX-RR) 1m 35.175s +0.818s [15/17] 299km/h 9. Andrea Dovizioso ITA Ducati Team (Desmosedici GP15) 1m 35.223s +0.866s [13/13] 315km/h 10. Danilo Petrucci ITA Octo Pramac Racing (Desmosedici GP14.1) 1m 35.271s +0.914s [7/21] 304km/h 11. Jack Miller AUS CWM LCR Honda (RC213V-RS)* 1m 35.348s +0.991s [16/18] 298km/h 12. Cal Crutchlow GBR CWM LCR Honda (RC213V) 1m 35.393s +1.036s [17/19] 305km/h 13. Andrea Iannone ITA Ducati Team (Desmosedici GP15) 1m 35.400s +1.043s [12/20] 312km/h 14. Stefan Bradl GER Athina Forward Racing (Forward Yamaha) 1m 35.486s +1.129s [20/20] 303km/h 15. Yonny Hernandez COL Octo Pramac Racing (Desmosedici GP14.2) 1m 35.924s +1.567s [14/15] 303km/h 16. Nicky Hayden USA Aspar MotoGP Team (RC213V-RS) 1m 35.965s +1.608s [14/15] 297km/h 17. Scott Redding GBR Estrella Galicia 0,0 Marc VDS (RC213V) 1m 36.158s +1.801s [12/21] 303km/h 18. Eugene Laverty IRL Aspar MotoGP Team (RC213V-RS)* 1m 36.223s +1.866s [18/22] 299km/h 19. Hector Barbera ESP Avintia Racing (Desmosedici GP14 Open) 1m 36.233s +1.876s [15/16] 307km/h 20. Alvaro Bautista ESP Factory Aprilia Gresini (RS-GP) 1m 36.250s +1.893s [16/18] 302km/h 21. Loris Baz FRA Athina Forward Racing (Forward Yamaha)* 1m 36.423s +2.066s [16/18] 299km/h 22. Mike Di Meglio FRA Avintia Racing (Desmosedici GP14 Open) 1m 36.619s +2.262s [15/18] 303km/h 23. Alex De Angelis RSM E-Motion IodaRacing (ART) 1m 37.486s +3.129s [9/18] 293km/h 24. Marco Melandri ITA Factory Aprilia Gresini (RS-GP) 1m 37.933s +3.576s [16/17] 296km/h

Marquez letting his Honda go as he approaches tyre wall after running off on out lap in FP1 at Assen #DutchGP pic.twitter.com/TopYolbJuR-- Crash.net MotoGP (@crash_motogp) June 25, 2015

Blue Name = Factory

Black Name

Red Name = Open

20 litres of race fuel, 5 engine changes for the season. All engines identical throughout the year within the same team (development freeze).Applicable to Factory entries by a manufacturer that did not achieve a dry win in 2013 (Ducati) or any new MotoGP manufacturers (Suzuki and Aprilia).22 litres of race fuel for Ducati, 24 litres for Suzuki and Aprilia. Same 12 engine changes, softer rear tyre, no engine development freeze and extra testing opportunities as the Open Category. Fuel and soft tyre can change depending on top three results.24 litres of race fuel, 12 engine changes, softer rear tyre, no engine development freeze and greater testing opportunities relative to Factory.