The Spaniard, quickest almost without exception across the Italian Grand Prix weekend, ended the day with a 1m47.435s.
He was not joined by team-mate Ben Spies, who missed the test due to the bout of food poisoning which also affected his form in Sunday's race. Lorenzo was easily able to complete Yamaha's modest test programme, aimed at finding small electronic improvements, and wrapped his testing duties up early.
That workload was in stark contrast to Honda, which brought a brand new bike - originally intended to be its 2013 MotoGP chassis - in an attempt to rectify its current tyre issues. Dani Pedrosa, second to Lorenzo on Sunday, repeated the trick at the day's end, edging out team-mate Casey Stoner by just two thousandths of a second.
Ducati meanwhile spent the day trialling engine modifications in an effort to improve drive and traction out of corners.
Nicky Hayden ended the day fourth fastest, but there was less positive news for Valentino Rossi, who fell one lap into the afternoon's running. Though he was unhurt, ECU issues prevented him from any further running.
The Italian's fall was one of three in the afternoon, with Pedrosa and LCR Honda's Stefan Bradl also down, although all three were unhurt.
Bradl, testing a variety of different parts, set the seventh fastest time, narrowly behind the Tech 3 duo of Cal Crutchlow and Andrea Dovizioso.
Of the CRT teams which did stay for the test, Forward Racing tested several different chassis against the Suter-BMW they currently use. Avintia also had a new FTR chassis to get to grips with.