The Aprilia Racing rider claimed victory on home ground in a time of 38 minutes 58.471 ahead of Carlos Checa, who came in 0.305s behind the Italian having begun the race 16th on the track.
Biaggi managed to hold off Checa's challenge despite the Spaniard recording the fastest lap of the race, 1:36.080.
Davide Giugliano came in third, 4.503s behind the winner, ensuring that both Italy and the Althea Ducati team had two representatives on the podium.
Biaggi is atop the standings with 185.5 points, 30 ahead of Tom Sykes (Kawasaki Racing), who moves up to second after finishing fourth having started on pole.
Marco Melandri (BMW Motorrad) slipped down from second in the championship standings to fifth as he was one of four riders who did not finish the race.
Full Race One results
1. Max Biaggi ITA Aprilia Racing RSV-4 38m 58.471s
2. Carlos Checa ESP Althea Ducati 1098R +0.305s
3. Davide Giugliano ITA Althea Ducati 1098R +4.503s
4. Tom Sykes GBR Kawasaki Racing ZX-10R +8.858s
5. Jonathan Rea GBR Honda WSBK CBR1000RR +11.627s
6. Chaz Davies GBR ParkinGO MTC Aprilia RSV-4 +12.258s
7. Eugene Laverty IRL Aprilia Racing RSV-4 +12.551s
8. Sylvain Guintoli FRA Effenbert Liberty Ducati 1098R +13.561s
9. Jakub Smrz CZE Liberty Effenbert Ducati 1098R +17.014s
10. Leon Camier GBR Crescent Fixi Suzuki GSX-R1000 +18.361s
11. Ayrton Badovini ITA BMW Italia Goldbet S1000RR +20.029s
12. Leon Haslam GBR BMW Motorrad S1000RR +22.082s
13. Maxime Berger FRA Effenbert Liberty Ducati 1098R +22.966s
14. Michel Fabrizio ITA BMW Italia Goldbet S1000RR +27.014s
15. Matteo Baiocco ITA Barni Ducati 1098R +31.133s
16. Hiroshi Aoyama JPN Honda WSBK CBR1000RR +31.719s
17. John Hopkins USA Crescent Fixi Suzuki GSX-R1000 +31.902s
18. Niccolo Canepa ITA Red Devils Ducati 1098R +43.770s
19. Leandro Mercado ARG Pedercini Kawasaki ZX-10R +55.071s
20. Federico Sandi ITA Grillini Progea BMW S1000RR +6 laps
21. Marco Melandri ITA BMW Motorrad S1000RR 21 laps completed
22. Loris Baz FRA Kawasaki Racing ZX-10R 13 laps completed
23. David Salom ESP Pedercini Kawasaki ZX-10R 8 laps completed
24. Lorenzo Zanetti ITA PATA Ducati 1098R 6 laps completed