Jorge Lorenzo sets record pace in first Mugello practice
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.
Rossi revealed on Thursday that he has reached what would be a record breaking 350km/h during private testing at Mugello on the GP12. The highest top speed this morning was 345.5km/h by Barbera.
The highest official top speed, which must be recorded during a grand prix event, stands at 349.3km/h (217.04mph) - set at Mugello by Pedrosa in 2009.
Cardion AB Ducati's Karel Abraham, who suffered left hand injuries sustained in testing at Aragon, is missing Mugello, but unlike last weekend at Sachsenring he has not been replaced by Franco Battaini.
Lorenzo has won four races this year, Stoner (-20 points) three and Pedrosa (-14 points) one. Pedrosa has finished every race, while Lorenzo and Stoner have each suffered one DNF.
The session was held in dry and bright conditions, but with dark clouds on the horizon. Second practice takes place this afternoon.
Friday practice (1):
1. Jorge Lorenzo
2. Casey Stoner
3. Dani Pedrosa
4. Nicky Hayden
5. Cal Crutchlow
6. Andrea Dovizioso
7. Valentino Rossi
8. Hector Barbera
9. Ben Spies
10. Stefan Bradl
11. Alvaro Bautista
12. Randy De Puniet
13. Aleix Espargaro
14. Mattia Pasini
15. Michele Pirro
16. Yonny Hernandez
17. Colin Edwards
18. Danilo Petrucci
19. James Ellison
20. Ivan Silva
