Jorge Lorenzo set the fastest time of the opening MotoGP practice session ahead of this weekend's race at Brno.
The championship leader bettered Valentino Rossi's benchmark with 20 minutes remaining and then improved his time to pull more than half a second clear at the head of the field.
Dani Pedrosa had been quickest early on and responded to Lorenzo's final push to move up to second, just ahead of Rossi. Andrea Dovizioso, Nicky Hayden and Colin Edwards completed the top six, with Casey Stoner 1.3sec slower than Lorenzo in seventh place.
There were no improvements in the last quarter of the session as a light rain descended on the Czech circuit and nobody took the risk.
Marco Simoncelli was the only faller, dropping his Gresini Honda into the gravel inside the first 10 minutes. Ben Spies and Alvaro Bautista rounded out the top 10.