Lorenzo quickest in opening practice

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 1.3 seconds 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.

Pos  Rider             Team               Time       Gap
 1.  Jorge Lorenzo     Yamaha             1m57.215s
 2.  Dani Pedrosa      Honda              1m57.756s  + 0.541s
 3.  Valentino Rossi   Yamaha             1m57.821s  + 0.606s
 4.  Andrea Dovizioso  Honda              1m57.873s  + 0.658s
 5.  Nicky Hayden      Ducati             1m58.286s  + 1.071s
 6.  Colin Edwards     Tech 3 Yamaha      1m58.497s  + 1.282s
 7.  Casey Stoner      Ducati             1m58.532s  + 1.317s
 8.  Marco Simoncelli  Gresini Honda      1m58.840s  + 1.625s
 9.  Ben Spies         Tech 3 Yamaha      1m58.970s  + 1.755s
10.  Alvaro Bautista   Suzuki             1m59.204s  + 1.989s
11.  Loris Capirossi   Suzuki             1m59.216s  + 2.001s
12.  Aleix Espargaro   Pramac Ducati      1m59.254s  + 2.039s
13.  Mika Kallio       Pramac Ducati      1m59.289s  + 2.074s
14.  Marco Melandri    Gresini Honda      1m59.510s  + 2.295s
15.  Hector Barbera    Aspar Ducati       1m59.910s  + 2.695s
16.  Randy de Puniet   LCR Honda          2m00.184s  + 2.969s
17.  Alex de Angelis   Interwetten Honda  2m01.098s  + 3.883s