Honda's Casey Stoner had dominated most of the morning's practice, setting an early 1m35.465s lap that left the rest squabbling over second.
That position was held in turn by Lorenzo, the Tech 3 Yamaha of Andrea Dovizioso, Stoner's team-mate Dani Pedrosa, Gresini Honda rider Alvaro Bautista, 2011 Assen winner Ben Spies (Yamaha) and then Lorenzo again.
The championship leader closed to within 0.085 seconds of the world champion, only for the Australian to improve to a 1m35.181s and reopen a 0.369s cushion.
But on Lorenzo's final run he first got Stoner's advantage down to 0.032s then threw in a 1m35.106s lap to grab practice one honours.
Pedrosa then squeezed in between Lorenzo and Stoner with a lap 0.026s off the pace, as just 0.075s covered the top three.
Spies ended up fourth, followed by the leading Ducati of Nicky Hayden, Bautista, Pramac Ducati's Hector Barbera, Tech 3 duo Dovizioso and Cal Crutchlow, and the second works Ducati of Valentino Rossi in 10th.
1 Jorge Lorenzo 1:35.106
2 Dani Pedrosa +00.020
3 Casey Stoner +00.075
4 Ben Spies +00.449
5 Nicky Hayden +00.735
6 Alvaro Bautista +00.761
7 Hector Barbera +00.864
8 Andrea Dovizioso +00.889
9 Cal Crutchlow +00.925
10 Valentino Rossi +00.978