The defending champion continued his impressive mid-season form with a best lap of one minute 22.056 seconds in warm conditions in Friday's second session.
The Yamaha rider's display served to increase the pressure on championship leader Casey Stoner, who has seen his lead at the top of the standing reduced to 15 points after finishing behind Lorenzo in the past two rounds.
Stoner clocked the fastest time in the morning, but struggled to improve on that in the afternoon and had to be content with the third best lap of the day, some 0.175secs behind Lorenzo.
Stoner's Repsol Honda team-mate Dani Pedrosa split the duelling riders to take second place.
Andrea Dovizioso was the fourth quickest with a best circuit of 1min 22.537secs ahead of local hopeful Ben Spies on his home track.
San Carlo Honda Gresini' Marco Simoncelli was sixth on the time charts and along with next best-placed Alvaro Bautista improved his morning session time by almost half a second.
Former MotoGP champion Valentino Rossi, who has Crew Chief Jeremy Burgess back in the garages after a two-race absence, had to be content with 11th place just behind his Ducati team-mate Nicky Hayden.