Alex Marquez came out on top in Friday's first free practice for the weekend's Teruel MotoGP, finishing the opening session almost half a second ahead of fellow Honda rider Takaaki Nakagami.
Marquez, the brother of six-time MotoGP champion Marc who is sitting out this season injured, posted a best lap of one minute, 48.184 seconds in Alcaniz, 0.438sec in front of Japan's Nakagami.
Championship leader Joan Mir posted the third fastest time, 0.809sec back as the Suzuki rider prepares to defend his wafter thin lead at the top of the standings in Sunday's race.
Mir is just six points ahead of France's Fabio Quartararo, with Maverick Vinales and Andrea Dovizioso both within 15 points of the Spaniard.
Quartararo, 21, finished 17th in the opening session, 1.437sec behind Mir and just behind Ducati's Dovizioso.
The second free practice session will start at 1230 GMT.
Times from the opening free practice session for the Teruel MotoGP on Friday:
1. Alex Marquez (ESP/Honda) 1min 48.184sec, 2. Takaaki Nakagami (JPN/Honda-LCR) at 0.438, 3. Joan Mir (ESP/Suzuki) 0.809, 4. Stefan Bradl (GER/Honda) 0.819, 5. Franco Morbidelli (ITA/Yamaha-SRT) 0.916, 6. Maverick Vinales (ESP/Yamaha) 0.992, 7. Jack Miller (AUS/Ducati-Pramac) 1.027, 8. Aleix Espargaro (ESP/Aprilia) 1.121, 9. Pol Espargaro (ESP/KTM) 1.162, 10. Cal Crutchlow (GBR/Honda-LCR) 1.172
16. Andrea Dovizioso (ITA/Ducati) 1.32, 17. Fabio Quartararo (FRA/Yamaha-SRT) 1.437