Lorenzo, who started from pole position, extends his overall world championship lead after his third win of the season in five races.
The 23-year-old is favourite for the title after team-mate Valentino Rossi broke his leg in practice for the Italian Grand Prix two weeks ago.
Results (with rider, country, bike and time):
MotoGP
1. Jorge Lorenzo, Spain, Yamaha, 41 minutes, 34.083 seconds, 170.4 kph.
2. Andrea Dovizioso, Italy, Honda, 41:40.826.
3. Ben Spies, United States, Yamaha, 41:41.180.
4. Nicky Hayden, United States, Ducati, 41:41.397.
5. Casey Stoner, Australia, Ducati, 41:41.577.
6. Randy De Puniet, France, Honda, 41:43.138.
7. Marco Simoncelli, Italy, Honda, 41:48.508.
8. Dani Pedrosa, Spain, Honda, 41:49.396.
9. Colin Edwards, United States, Yamaha, 42:02.037.
10. Aleix Espargaro, Spain, Ducati, 42:16.477.
Standings (After 5 of 18 races):
1. Jorge Lorenzo, Spain, Yamaha, 115.
2. Andrea Dovizioso, Italy, Honda, 78.
3. Dani Pedrosa, Spain, Honda, 73.
4. Valentino Rossi, Italy, Yamaha, 61.
5. Nicky Hayden, United States, Ducati, 52.
250cc
1. Jules Cluzel, France, Suter, 39 minutes, 19.472 seconds, 162.1 kph.
2. Thomas Luthi, Switzerland, Moriwaki, 39:19.529.
3. Julian Simon, Spain, Suter, 39:19.794.
4. Scott Redding, Britain, Suter, 39:19.992.
5. Alex Debon, Spain, FTR, 39:24.743.
6. Shoya Tomizawa, Japan, Suter, 39:24.849.
7. Mike Di Meglio, France, Suter, 39:24.956.
8. Xavier Simeon, Belgium, Moriwaki, 39:25.181.
9. Dominique Aegerter, Switzerland, Suter, 39:29.712.
10.Toni Elias, Spain, Moriwaki, 39:29.883.
Standings (After 5 of 18 races):
1. Toni Elias, Spain, Moriwaki, 80 points.
2. Shoya Tomizawa, Japan, Suter, 65.
3. Thomas Luthi, Switzerland, Moriwaki, 58.
4. Julian Simon, Spain, Suker, 51.
5. Simone Corsi, Italy, Motobi, 51.