A day after making his first televised 147 break, the defending champion headed into the clash as tournament favourite but he was well below his best during a 5-3 defeat which ends his bid to reach a fourth successive final.
Vafaei managed two century breaks - 106 and 100 - as well as runs of 74 and 57 during the biggest victory of his career and he'll now meet Mark Williams, who stunned Shaun Murphy 5-1, in Saturday's semi-finals.
Iran’s only professional player is only 22 yet never seemed fazed by the pressure, with his 106 break coming in the penultimate frame, and he'll now aim to reach the first ranking final of his career.
Welsh veteran Williams gave his chances of qualifying for the World Championship a shot in the arm with a superb victory over Murphy.
The two-time China Open champion needs to claim the title for a third time to leapfrog Ryan Day into the world's top 16 and secure an automatic place at the Crucible.
His top break of 52 arrived in the sixth frame of a scrappy match and afterwards he said: "Nobody wants to go to the qualifiers. However, I put my mind to it about two or three months ago that it was more than likely that I would be there.
"I’d love to get to another final, it’s been a while. If I won it would be fantastic. To have already won this event twice is unbelievable but if I could make it a third it would be extra special."
In the afternoon quarter-finals, Mark Selby thrashed Stephen Maguire 5-1 while Kyren Wilson progressed by the same scoreline against Ding Junhui.
China Open: Friday results & weekend schedule
Click here for full tournament results
Friday March 31
Afternoon Session (0700 BST)
Quarter-Finals (Best of 9 frames)
Judd Trump 3-5 Hossein Vafaei (QF 1)
Shaun Murphy 1-5 Mark Williams (QF 2)
Evening Session (1230 BST)
Quarter-Finals (Best of 9 frames)
TV Coverage: Eurosport 1/Quest
Kyren Wilson 5-1 Ding Junhui (QF 3)
Stephen Maguire 1-5 Mark Selby (QF 4)
Saturday April 1
Afternoon Session (0700 BST)
Semi-Finals (Best of 11 frames)
TV Coverage: Eurosport 1/Quest
Hossein Vafaei v Mark Williams (SF 1)
Evening Session (1230 BST)
Semi-Finals (Best of 11 frames)
TV Coverage: Eurosport 1/Quest
Kyren Wilson v Mark Selby (SF 1)
Sunday April 2
Afternoon Session (0700 GMT)
Final, first session (Best of 19 frames)
TV Coverage: Eurosport 1/Quest
Hossein Vafaei/Mark Williams v Kyren Wilson/Mark Selby
Evening Session (1230 BST)
Final, second session (Best of 19 frames)
TV Coverage: Eurosport 1/Quest
Hossein Vafaei/Mark Williams v Kyren Wilson/Mark Selby
