"I haven't fully realised yet what I just did," the 25-year-old Fortunato said, having claimed his first victory in more than eight years, having last won as a junior.
Bennett, who is striving to become the first New Zealander to win a stage of the Giro, came home fifth from the breakaway, but was caught by two riders from the peloton, with race leader Egan Bernal and the improving Simon Yates riding by him in the final kilometre.
The 31-year-old rued doing too much work in the breakaway before the climb began, which combined with inclement weather left him short on power on the Zoncolan.
"Unfortunately I didn't have the legs to compete for the stage victory", Bennett said. "It was a really tough stage. We went full throttle from the start and there was a lot of headwind. We had to fight for every second to stay ahead. Edoardo was really strong and he deserves all the credit, because he made the difference on the flat. As a result I didn't have the power anymore at the beginning of the Zoncolan."
"We had a clear plan and that was to go for the stage win with George or Koen [Bouwman]", Jumbo-Visma sports director Arthur van Dongen added. "In the flat approach the plan was also to have Edoardo in the breakaway for support. That went perfectly according to plan. Edoardo did a fantastic job, but because Astana increased the pressure from behind it cost George, in particular, a little too much energy on the flat.
"He paid the price on the Zoncolan. That is a pity because normally such a climb suits him."
Bennett's ride moved him into 18th overall, and should still have leeway to participate in breakaways in the final week, as he is still 11 minutes and 48 seconds behind Bernal, who is storming away with the Giro.
Bernal responded to a late attack from Yates and then attacked the British rider in the fog at the summit to finish fourth and extend his overall lead to a significant one minute, 33 seconds ahead of Yates, who moved into second.
"I tried to remain calm when we tackled the Zoncolan because I knew I was in a good position in the GC and did not need to attack first," said Bernal. "I followed Simon Yates when he attacked and then I did an acceleration in the finale.
"I think I did a good race. Now I have a good lead but I need to remain calm and focused, anything can happen in the Giro."