Kirk Shepherd stunned Wayne Mardle 6-4 to set up a PDC World Darts final against John Part on New Year's Day.
Mardle was tipped to see off the Kent qualifier after downing 13-time world champion Phil Taylor in the last eight.
He took the first set 3-0, but Shepherd refused to be intimidated and led 3-1 before Mardle fought back to 4-4, but Shepherd held his nerve to triumph.
Canadian Part had earlier booked his place in the final with a resounding 6-2 win over Kevin Painter.
The former PDC and BDO title-holder raced into a 5-1 lead in their best of 11 sets semi-final before Painter pegged him back to 5-2.
"I'm on cloud nine - I'm pinching myself all the time"
Part, whose nickname is "Darth Maple", survived a minor eighth-set wobble at 2-2 to close out the contest with an ice-cool 130 check-out.
"It was a tough match all the way through," said Part.
"There's a lot of respect between the two of us. I think we were both very tight, but I probably hit more important darts than he did."
But the evening belonged to Shepherd, a 21-year-old sheet metal worker from Ramsgate, who dashed Mardle's title hopes for another year.
The 34-year-old from Dagenham has now lost at the semi-final stage of the PDC World Championships four times.
"Young Gun" Shepherd, rated as a 500-1 outsider at the start of the tournament, could become the first qualifer to become world champion since Keith Deller upset Eric Bristow 25 years ago.
And he said he would not be content with just a place in the final.
"I'm on cloud nine - I'm pinching myself all the time," he said.
"I believe I can do it - I know I can win this."
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