Vafaei, who punished a missed match ball from Judd Trump in Thursday's quarter-final, was guilty of letting victory slip from his fingers as he missed a difficult pink that would have given him a 7-5 win.
Un-Nooh made him pay as a number of snookers settled the deciding frame to put the Thai into his third final in eight years.
The 2015 champion will face 2016 winner Ding, who secured his place with a 7-4 win over Tom Ford in the second semi-final.
A missed yellow allowed Ford to come from 4-1 down and level the match with a break of 70 in the eighth frame, but Ding soon reimposed himself with breaks of 70 and 64 setting up victory.
Both players are hoping to join Mark Davis and Stephen Maguire as the only multiple winners of this event.
