He set a new lap record in the process as he cruised to victory, and was even able to wave to the crowd in celebration with half a lap remaining.
Lorenzo told BBC Sport: "We had bad luck in the last few races but all weekend here we were very competitive.
"I was focused and I made no mistakes at all. Little by little I gained confidence and was able to open up a big gap."
MotoGP: Jorge Lorenzo thanks lucky helmet for Mugello win
Crutchlow and Rossi -
who could be team-mates at Ducati
next season - were fighting for sixth place for most of the race but both were able to pass Nicky Hayden on the final lap after he was shoved wide by Stefan Bradl, who finished fourth.
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