Casey Stoner knocked Ben Spies from the top of the first practice timesheets at Misano, on his very last lap of Friday morning's session.
The MotoGP title leader finished 0.286sec clear of Yamaha rider Spies, with Dani Pedrosa - who led much of the session - and Andrea Dovizioso making it three Repsol Hondas in the top four.
Gresini Honda's Marco Simoncelli was fifth, with Yamaha's reigning champion Jorge Lorenzo - who struggled last weekend at Indianapolis - getting off to another slow start in sixth, 0.962sec from title rival Stoner.
Aspar Ducati's Hector Barbera was the leading satellite rider in seventh, but 1,.3sec from the top, followed by Suzuki's Alvaro Bautista, Tech 3 Yamaha's Colin Edwards and Cardion AB Ducati's Karel Abraham.
Home hero Valentino Rossi was only eleventh, and the third best Ducati, having been left 1.565sec from Stoner. Tech 3's Cal Crutchlow split the two factory Desmosedicis, with Nicky Hayden in 13th.
Hiroshi Aoyama (Gresini), the soon to retire Loris Capirossi (Pramac), Randy de Puniet (Pramac) and Toni Elias (LCR) completed the order.
Second practice takes place this afternoon.
Friday practice (1):
6. Lorenzo 0.962
11. Rossi 1.565
16. de Puniet