The Italian national time trial champion completed the course in a lightning fast 22 minutes and 24 seconds, 23 seconds quicker than his closest competitor Thymen Arensman (Team DSM).
Sobrero's win marked a time trial clean sweep for team BikeExchange Jayco following Simon Yates' Stage 2 win in Budapest.
"There's big emotions for me," Sobrero told SBS following the stage.
"To finish the Giro with a win, especially in the national champion jersey, it's really special."
Sobrero was the quickest to the summit of the 4.5 kilometre climb at the midway point of the course, but encountered water on the road on the descent, which he said worried him at first but didn't allow him to lose sight of winning the stage.
"Before the start, I was told the descent was wet, and I was a bit afraid," he said.
"I thought maybe it wasn't my day, but I said 'I'll give everything on the climb and will have to see how the descent goes.
"Then when I took the first few corners, I saw that it was wet but still okay and maybe it was my day.
"I just tried to go into the corners really fast and as safe as possible and it was good."
Sobrero also revealed he had received support from good friend and fellow Italian time trial specialist Filippo Ganna (INEOS Grenadiers) who no doubt gave him some tips having taken out last year's opening time trial at the Giro.
"I'm quite sure he (Ganna) was watching me on TV," Sobrero said.
"I think he's proud of me today. We've been talking a lot during these three weeks.
"He's in training camp preparing for the Tour [de France], so I wish him the best of luck for that."
