Two-time champion Ted Hankey crashed out of the BDO World Championships after a semi-final defeat to Christian Kist before announcing he was
quitting the organisation to join the PDC Tour.
Hankey lost 6-5 having led 5-3, claiming his aim was affected when the air conditioning was turned on.
"The Count" narrowly missed a bullseye for the match at 5-4 before Kist's stunning fightback.
is also through to Sunday's final after beating Wesley Harms 6-5.
Kist started the match strongly, taking a 2-1 lead, but Hankey slowly began to find his rhythm and looked to have the contest wrapped up when he clinched the eighth set to lead 5-3.
Beaten semi-finalist Ted Hankey
“I know why [the air conditioning] came on but I'm not going to say in front of the camera. I'm not happy about it and I will see people about it”
Kist comfortably won the ninth to reduce the deficit to 5-4 before Hankey had a shot at the bull to win the match in a nerve-jangling 10th set, only for his dart to land just the wrong side of the wire.
"The Lipstick" stole that set to level the scores at 5-5 and calmly took the final set to love as Hankey lost his cool, tossing away several darts in anger and twice complaining to officials about a draught on the oche.
Qualifier Kist was shocked to reach the final at his first attempt: "I really can't find the words to say how I feel. It's a surprise, I cannot believe it. I never give up, I just keep going on and on."
Speaking to BBC Sport's Colin Murray after the match, a visibly shaken Hankey said: "At 5-3 I was in control but then the air conditioning came on.
DID YOU KNOW?
- Ted Hankey uses 14 gram darts, one of the lightest on the circuit
"I know why it came on but I'm not going to say in front of the camera. I'm not happy about it and I will see people about it."
He said the time had come to switch to Barry Hearn's PDC Tour, adding: "This is it for me. Thanks a lot to everyone. I've had great support here but times change, I've made my decision.
"I'll miss this place, you can't explain the Lakeside atmosphere, but it's time to move on."
In the other semi-final, O'Shea won the first set before Dutchman Harms bounced back to win three of the next four and establish a 3-2 lead.
O'Shea, who lost to Hankey in the 2009 World Championship final, refused to back down, winning three of the next four sets to edge 5-4 ahead.
Harms levelled at 5-5 before both players, like Hankey, asked organisers to investigate a draught. This time, the match was suspended.
The board was also changed with the players suffering a combined total of 23 bounce-outs.
When the players returned for the decider, it was O'Shea who settled the quicker of the two, with "The Silverback" going on to win the set 3-1 and reach his second World Championship final.
"It is unbelievable, I am so overwhelmed," said O'Shea. "That young lad [Harms] has got a great future.
"It was he who suggested that we change the board because I had suffered so many bounce-outs. He is a real gentleman."
O'Shea beats Harms to reach BDO final
2012 BDO World Darts Championships final: Christian Kist v Tony O'Shea, Sunday 15 January.
Watch live on BBC Two
from 1745 GMT