Championship leader Jorge Lorenzo of Spain dominated practice on his Yamaha despite windy conditions during the first two sessions on Friday ahead of this weekend's Italian Grand Prix.
Lorenzo, winner on the Mugello circuit last season, clocked a fastest lap of 1min 48.076sec, despite an early run-off into the gravel.
Spaniard Dani Pedrosa was second quickest on a Honda at 0.031sec behind Lorenzo with US Ducati rider Nicky Hayden third fastest at 0.081.
"I'm really happy because from the beginning we've been quite fast. We haven't had to make many changes to the bike, the feeling is great with the track and it's working well," said Lorenzo.
"I feel good with the suspension, throttle and braking. Everything seems quite clear, we have to work on some small details but we've made an excellent beginning." Spanird Hector Barbera of Ducati came back after a crash mid-way through the session, which briefly saw practice red-flagged, to set the fourth fastest time.
Fifth spot went to Yamaha's Andrea Dovizioso, bidding for his fourth podium finish this season at his home race. Repsol Honda's Casey Stoner finished the day in sixth, with Lorenzo's teammate Ben Spies in seventh.
In eighth, Dovizioso's teammate Cal Crutchlow was just over half a second off the front, as the battle looks set to be heated on the Tuscany track.
Ducati's Valentino Rossi, a seven-time winner at home between 2002 and 2008, was ninth fastest.