The Englishman raced into a 2-0 lead that included a break of 113 in the second frame - the 1,228th century of his illustrious career.
Vafaei did pull it back to 2-2 against the player he describes as his "hero", but failed to capitalise on his chances after the interval and was ultimately swept away after the resumption.
"Every day is different, today was my worst day," Vafaei told Eurosport. "I don't have that heart to play against my hero, to go and kill, you know?
"I lost to my hero. There was only one man who could stop me in this tournament and it was Ronnie O'Sullivan.
"To be honest, when I look at my path, where I am standing right now, that means how far I came. I'm playing against my hero. I came so far, I'm so proud of myself."
Vafaei will also miss out on a place at The Masters as a result of the defeat.
It wasn't the prettiest snooker from the Rocket, but he now goes into Sunday's final as the likely favourite to take the crown for an eighth time.
"It was all right," O'Sullivan told Eurosport after his victory. "It was acceptable, I suppose, something to work with. The dynamic stuff wasn't there but it doesn't have to be sometimes, steady is all right.
"He made my job a little bit easier."