Dani Pedrosa edged out 2012 MotoGP title rival Jorge Lorenzo to set the pace in the opening MotoGP practice session at Brno.
The two Spaniards are effectively the only men in contention for this year's world championship following Casey Stoner's decision to leave Brno and fly home for ankle surgery.
There was little to choose between the pair in the opening practice session of the Czech Grand Prix, although Pedrosa's best of 1m59.003s was ultimately enough to earn him top spot, just over one tenth of a second ahead of Lorenzo.
There was a moment of drama for the Honda man however, as a stone thrown up when Valentino Rossi ran wide and through the dirt hit him on the foot.
He was visibly limping as he headed back into the pits and pulled into his garage, although he was later able to rejoin the track and set his fastest time.
The debris churned up by Rossi's Ducati also caused a brief red flag session to clear the circuit.
When it did resume, the two Tech 3 Yamaha bikes managed to close on the lead pair, with Andrea Dovizioso - who will move to Ducati from 2013 - heading team-mate Cal Crutchlow.
Ben Spies completed a happy session for Yamaha by taking fifth on the second works bike, less than half a second down on Pedrosa.
Gresini Honda's Alvaro Baustita also got within five tenths of the Spaniard, while Valentino Rossi in seventh finished 1.168s down.
LCR Honda rider Stefan Bradl finished eighth, ahead of the CRT duo of Randy de Puniet (Aspar) and Yonny Hernandez (Avintia).
Alongside Stoner, Ducati's Nicky Hayden and Pramac's Hector Barbera will miss this weekend due to injuries suffered at Indianapolis.
Pos Rider Team/Bike Time Gap 1. Dani Pedrosa Honda 1m57.003s 2. Jorge Lorenzo Yamaha 1m57.149s + 0.146s 3. Andrea Dovizioso Tech 3 Yamaha 1m57.189s + 0.186s 4. Cal Crutchlow Tech 3 Yamaha 1m57.418s + 0.415s 5. Ben Spies Yamaha 1m57.446s + 0.443s 6. Alvaro Bautista Gresini Honda 1m57.501s + 0.498s 7. Valentino Rossi Ducati 1m58.171s + 1.168s 8. Stefan Bradl LCR Honda 1m58.345s + 1.342s 9. Randy de Puniet Aspar Aprilia 1m58.667s + 1.664s 10. Yonni Hernandez AvintiaFTR-Kawasaki 1m59.256s + 2.253s 11. Karel Abraham Cardion Ducati 1m59.256s + 2.253s 12. Aleix Espargaro Aspar Aprilia 1m59.504s + 2.501s 13. Toni Elias Pramac Ducati 1m59.881s + 2.878s 14. Mattia Pasini Speed Master Aprilia 2m00.206s + 3.203s 15. Colin Edwards Forward Suter-BMW 2m00.531s + 3.528s 16. Michele Pirro Gresini FTR-Honda 2m00.715s + 3.712s 17. Ivan Silva Avintia Inmotec-Kawasaki 2m01.302s + 4.299s 18. James Ellison Paul Bird Aprilia 2m02.171s + 5.168s 19. Danilo Petrucci Ioda-Aprilia 2m02.244s + 5.241s