MotoGP title leader Jorge Lorenzo
lapped under the official Mugello race lap record on his way to claiming a 0.5s advantage in Friday morning's opening practice for the Italian Grand Prix.
Lorenzo was quickest for much of the 45-minutes, with his best lap of 1m 48.131s set on the last of his 17 laps.
That beat the Factory Yamaha rider's own official race lap record of 1m 48.402s, set on his way to victory last season, and came close to Casey Stoner's 1m 48.034s pole record.
Reigning champion Stoner moved into a late second place for Repsol Honda after being as low as tenth for part of the session.
Stoner's last lap improvement put the Australian ahead of newly re-signed team-mate Dani Pedrosa
(+0.746s) - now Lorenzo's nearest tile rival after his first victory of the season last Sunday in Germany - with Nicky Hayden
stating his claim for a new Ducati contract in fourth place (+0.850s).
But while Lorenzo was leading the way, two of his fellow Yamaha riders suffered misfortune.
Tech 3's Cal Crutchlow was forced to park his M1 after suffering a technical problem with 14 minutes to go, before returning to snatch fifth position on his spare bike (+0.892s).
Lorenzo's team-mate Ben Spies was seen taking a scooter ride back to the paddock shortly after Crutchlow, following an unseen fall. Unable to return, the Texan finished the session in ninth place (+1.267s).
Italians Andrea Dovizioso
(Tech 3) and Valentino Rossi
(Ducati) were sixth and seventh, with Hector Barbera in eighth for Pramac. Honda LCR rookie Stefan Bradl completed the top ten, behind Spies.
The San Carlo Honda Gresini team is back in white colours this weekend, as tribute to the team's late Italian star Marco Simoncelli.
Alvaro Bautista ran on and fell in the turn one gravel in the closing stages, on his way to eleventh, with the team's CRT rider Michele Pirro in 15th out of the 20 riders.
The top CRT rider was Aspar's Randy de Puniet
(ART), in twelfth place and 1.2s from Bautista.