A photo-finish was required to separate Bennati, whose stage win was his third on the Giro, and British rider Mark Cavendish (High Road), who shot through to the finishing line after this 169km stretch from Forli to Carpi.
Third place was taken by Australian Robbie McEwen (Silence-Lotto) who shadowed Bennati without being able to overtake him.
The 27-year-old Tuscan Bennati said afterwards: "This is the first time I have won by three centimetres, but I have lost by that margin once before. It was also the first time I had led a sprint for such a long way and it was a risk because I was vulnerable to those behind me, who had me in their sights."
Bennati, who came out in front at the last corner to sprint the final 200 metres to add this to his wins in Milazzo (Stage 2) and San Vincenzo (Stage 9), added: "At the line, I was calm about things and I thought I had lost to Cavendish, (who) is a real sprinter in the final 150 metres with amazing explosive power."
Spaniard Dionisio Galparsoro (Euskaltel-Euskadi), who stands well off the pace in the overall standings, led a long sole breakaway from the start, building up a 14-minute advance on the peloton. But he was reeled back in with 10km to go.
When asked about how he compared with great sprinters such as Mario Cipollini and Alessandro Petacchi, Bennati added: "I'm not like those two because I have only won three stages while they have won so many. But I think I am a good guy and have won three of the four sprints since the start of the race."
Overall leader Visconti revealed he was not feeling great after falling in Wednesday's stage about 30 kilometres from the finish.
"I'm in pain all over my body after my fall," Visconti said. "I didn't sleep at all last night and during the stage I went to see the race doctor. Every time I went over a bump I had pain in my wrist and, though it's not broken, perhaps I will go and have some new X-rays."
Visconti leads overall by 5 minutes, 50 seconds from compatriot Gabriele Bosisio (LPR Brakes) and by 6:59 from Tour de France reigning champion Alberto Contador of Spain.
It was later revealed by race doctors that sixth-stage winner Matteo Priamo of Italy had fractured his right elbow in a fall about 15 kilometres from the finishing line of Thursday's stage. Italy's Mirco Lorenzetto, who also fell, was treated for multiple cuts and bruises at the finishing line.
Friday's 13th stage sees the riders tackle a 177km run between Modena and Cittadella.
For full results, report and photos, visit Cyclingnews.com.
© AFP 2008