Jorge Lorenzo set the pace in first practice for the Czech MotoGP at Brno as the session was dominated by the factory Fiat Yamaha squad.
The Spaniard, who crashed out the British Grand Prix at Donington last month, resisted session-long pressure from his championship-leading teammate Valentino Rossi to go quickest of all with a 1m56.595s lap, following a consistently rapid sequence of laps.
Rossi, who was quickest early-on until Lorenzo unleashed that volley of laps, could only manage second fastest with a 1m56.994s best on his final lap of the session.
HRC Honda rider Dani Pedrosa was third fastest after a late dash that put him 0.7sec slower than Rossi.
Colin Edwards stayed in touch for Tech 3 Yamaha in fourth, though he was more than 1.1sec away from Lorenzo's ultimate pace.
Donington winner Andrew Dovizioso improved to fifth fastest in the final minutes of the session ahead of another late flier Toni Elias, on the factory-spec Gresini Honda.
Mika Kallio was an impressive seventh fastest on the factory Ducati in his first stand-in session for the absent Casey Stoner. The Finn was more than half a second quicker than his teammate Nicky Hayden who was 12th quickest.
Alex de Angelis was eighth fastest despite crashing his Gresini Honda on the last lap of the session.
Suzuki's Loris Capirossi and Hayate Kawasaki's Marco Melandri completed the top 10.