Eugene Laverty followed up his maiden victory in race one with another in race two after a thrilling battle with teammate Marco Melandri.
The Yamaha team were handed a 1-2 position after long time leader Max Biaggi was controversially given a ride through penalty.
As in race one, it was Troy Corser who made it to the first corner first, with Biaggi slotting in behind in second with teammate Leon Camier storming from the third row of the grid up to third.
There was chaos behind as Leon Haslam crashed his BMW, with Jonathan Rea and Jakub Smrz unable to steer around the stricken bike. All three were out on the spot and appeared to have thwarted Laverty's victory hopes as the Irishman braked heavily to avoid the S1000 RR.
Biaggi took the lead from Corser at the end of lap one and disappeared into the distance, with Camier following through a couple of laps later.
The Aprilia Alitalia 1-2 lasted until lap eight, when Camier slid out of second place at the second Lesmo corner, promoting Melandri into second ahead of Michel Fabrizio, Noriyuki Haga and Laverty who had recovered to fifth.
The controversy came on lap eleven, when Max Biaggi outbraked himself into the first chicane, forcing him to take to the escape road.
Unfortunately for the World Champion, he set the fastest lap of the race in the process and was deemed to have gained an advantage. The livid Italian was handed a ride through penalty, and any hopes of a first win of 2011 were dashed.
Melandri inherited the lead but Laverty had fought his way up to second and was right on the tail of his teammate. Haga and Fabrizio were disputing the final podium position with Troy Corser close behind in fifth.
Laverty waited until the final lap to make his move. Melandri made an error through the Variante della Roggia but the Irishman chose to tuck in behind, with the Parabolica his chosen overtaking destination.
Laverty showed his nose but Melandri seemed to have things under control until he ran wide through the final corner, handing the 25 points on a plate for Laverty.
Fabrizio came out on top in the battle for third to claim his and Suzuki's first podium of the season with Haga and Corser also getting their best results of the season in fourth and fifth.
Ayrton Badovini gave BMW Motorrad Italia a top six result at their home event, edging ahead of Sylvain Guintoli, the leading Ducati.
Biaggi came home a frustrated eight but at least he fared better than championship rival Carlos Checa. The Spaniard lost his record of finishing on the podium at every event as Althea Ducati struggled for pace at the high speed circuit, trailing home in tenth behind Joan Lascorz.
Tom Sykes was the last remaining Briton in 11th, less than a second adrift of the championship leader whose lead has shrunk considerably.
Checa now has a 27 point advantage over Marco Melandri, with Biaggi a further point behind in third as he still searches for his first win of the year. After back-to-back wins, Laverty has leaped up to fifth in the standings, 60 points off the lead.
Race Result: 18 Laps:
| Pos | Rider | Team | Gap | Points |
| 1 | Eugene Laverty | Yamaha World Superbike Team | 18 Laps | 25 |
| 2 | Marco Melandri | Yamaha World Superbike Team | +0.327 | 20 |
| 3 | Michel Fabrizio | Team Suzuki Alstare | +2.486 | 16 |
| 4 | Noriyuki Haga | PATA Racing Team Aprilia | +2.583 | 13 |
| 5 | Troy Corser | BMW Motorrad Motorsport | +4.502 | 11 |
| 6 | Ayrton Badovini | BMW Motorrad Italia SBK Team | +10.865 | 10 |
| 7 | Sylvain Guintoli | Team Effenbert-Liberty Racing | +11.038 | 9 |
| 8 | Max Biaggi | Aprilia Alitalia Racing Team | +18.724 | 8 |
| 9 | Joan Lascorz | Kawasaki Racing Team | +20.093 | 7 |
| 10 | Carlos Checa | Althea Racing | +20.376 | 6 |
| 11 | Tom Sykes | Kawasaki Racing Team | +21.111 | 5 |
| 12 | Ruben Xaus | Castrol Honda | +28.608 | 4 |
| 13 | Roberto Rolfo | Team Pedercini | +33.459 | 3 |
| 14 | Mark Aitchison | Team Pedercini | +42.810 | 2 |
| 15 | Fabrizio Lai | Echo Sport Racing Company | +55.759 | 1 |
| Maxime Berger | Supersonic Racing Team | +5 Laps | ||
| Leon Camier | Aprilia Alitalia Racing Team | +11 Laps | ||
| Jakub Smrz | Team Effenbert-Liberty Racing | +18 Laps | ||
| Leon Haslam | BMW Motorrad Motorsport | +18 Laps | ||
| Jonathan Rea | Castrol Honda | +18 Laps | ||
| James Toseland | BMW Motorrad Italia SBK Team | Non Starter | ||
| Chris Vermeulen | Kawasaki Racing Team | Non Starter |
Riders Championship: After Round 4 (Italy)
| Pos | Rider | Team | Wins | Points |
| 1 | Carlos Checa | Althea Racing | 4 | 145 |
| 2 | Marco Melandri | Yamaha World Superbike Team | 1 | 118 |
| 3 | Max Biaggi | Aprilia Alitalia Racing Team | 117 | |
| 4 | Jonathan Rea | Castrol Honda | 1 | 89 |
| 5 | Eugene Laverty | Yamaha World Superbike Team | 2 | 85 |
| 6 | Leon Haslam | BMW Motorrad Motorsport | 84 | |
| 7 | Michel Fabrizio | Team Suzuki Alstare | 74 | |
| 8 | Leon Camier | Aprilia Alitalia Racing Team | 58 | |
| 9 | Jakub Smrz | Team Effenbert-Liberty Racing | 55 | |
| 10 | Noriyuki Haga | PATA Racing Team Aprilia | 47 | |
| 11 | Troy Corser | BMW Motorrad Motorsport | 46 | |
| 12 | Ayrton Badovini | BMW Motorrad Italia SBK Team | 35 | |
| 13 | Tom Sykes | Kawasaki Racing Team | 34 | |
| 14 | Joan Lascorz | Kawasaki Racing Team | 33 | |
| 15 | Ruben Xaus | Castrol Honda | 31 | |
| 16 | Sylvain Guintoli | Team Effenbert-Liberty Racing | 29 | |
| 17 | Roberto Rolfo | Team Pedercini | 15 | |
| 18 | Mark Aitchison | Team Pedercini | 9 | |
| 19 | Maxime Berger | Supersonic Racing Team | 5 | |
| 20 | Barry Veneman | BMW Motorrad Italia SBK Team | 3 | |
| 21 | Josh Waters | Yoshimura Suzuki Racing Team | 3 | |
| 22 | James Toseland | BMW Motorrad Italia SBK Team | 2 | |
| 23 | Bryan Staring | Team Pedercini | 1 | |
| 24 | Fabrizio Lai | Echo Sport Racing Company | 1 |
