Robert Thornton knocked reigning champion Phil Taylor out of the PartyPoker.com World Grand Prix with a stunning deciding leg victory at the Citywest Hotel.
After seeing Taylor win the first set 3-1, Thornton took the next two to move ahead - winning one with a 101 finish before following a 104 checkout with a 13-darter in the third set's decider.
The defending champion replied strongly to win the fourth set without reply and also led 2-1 in the fifth, only to miss a dart at the bull for the match as Thornton levelled to force a deciding leg.
Taylor hit a 177 to be first to a finish, but uncharacteristically missed five darts for the match to allow Thornton in to take out double top to reach the quarter-finals on Friday night.
"It's an outstanding result for me," said Thornton, the reigning UK Open champion and a former World Masters winner.
"The win ranks up there with the best of my career because it's a harder format.
Thornton now meets Mervyn King in Friday's quarter-finals.
King defeated Dave Chisnall 3-1 with a fine performance to book his place in the last eight of a major for the first time in almost 12 months.
Northern Ireland's Brendan Dolan, last year's runner-up, continued his love affair with the double-start tournament by knocking out Holland's Vincent van der Voort 3-1 to set up a quarter-final with Justin Pipe.
Pipe, meanwhile, defeated Kevin Painter 3-2 in a tight contest to book his place in only a second major quarter-final, with the win also set to move him into the world's top ten for the first time.