Barney was in confident form throughout the whole match
Raymond van Barneveld completed the first ever nine-dart finish in the PDC World Championship to crush Jelle Klaasen 5-1 and reach the last four.
The five-time world champion was in imperious form as he achieved the feat in the second leg of the sixth set and sealed victory with a 161 checkout.
Van Barneveld will face third seed James Wade in Saturday's semi-final.
Wade was less than impressive but still had too much for Australia-based Englishman Paul Nicholson, winning 5-3.
After struggling to beat Ronnie Baxter in the last 16 and losing the first set to his compatriot, Van Barneveld was under some pressure but upped his game to devastating effect.
He rattled off six legs in a row to go 2-1 ahead and then took a 3-1 lead thanks to a 91 checkout on the Klaasen throw.
From then on there was no way back for the 2006 BDO world champion, and Van Barneveld checked out on 116 and 96 on his way to taking the fifth set.
But the Dutchman saved the best until last with two consecutive 180s to start the second leg of the sixth set and with the Alexandra Palace crowd roaring him on, he hit another treble 20 and followed that up with treble 19 before sealing the feat with double 12.
It was the second nine-dart finish of Van Barneveld's career after he achieved it against Peter Manley in the Premier League in 2006 and it earns the Dutchman a £20,000 bonus.
"I was full of confidence despite losing the first set," he said afterwards. "I was getting in my own zone and I was so focused on that treble 20 all the time.
"To have a nine-darter in the World Championship is massive. I am very proud to become the first one to do it in this World Championship.
Wade struggled with an average of only 81.75 in the match
"I was lucky to be here after Ronnie missed with two darts for 67 to win the other night. But I have had to dig in deep this last year and keep believing in myself, and what I have done in the last few months has come out on the stage here."
The excitement of the all-Dutch encounter contrasted with the night's opening quarter-final where both players struggled to make an impact on the game.
Nicholson failed to take his chances early on as Wade claimed the opening two sets but Nicholson pulled a set back before Wade stretched his advantage again, thanks to checkouts of 135 and 64 en route to making it 3-1.
However, the third seed was broken at the start of the fifth set and went on to lose the next six legs to enable the world 126 to level the match at 3-3.
But Wade found a glimpse of form when he most needed it, hitting two successive 180s on his way to securing the seventh set before he completed the victory in the eighth with a double two.
"I'm pleased to have got through but it was a poor performance, much below the standard I set myself," said Wade.
"I don't know what went wrong, because I felt fine before the game, but I've got 24 hours to put it right."
The first semi-final on Saturday will see number one seed Phil Taylor take on Mervyn King.