Gerwyn Price surrendered a two-set lead as he exited the PDC World Darts Championship with a second-round defeat by Nathan Aspinall.
Price, the Grand Slam champion and sixth seed, had a dart to seal a straight-sets 3-0 win.
But Aspinall fought back - a 140 checkout sealing the fourth set - before taking the deciding set 3-0.
The session's other seeded players - Ian White (11), Jonny Clayton (15) and Jelle Klaasen (24) - also lost.
However, Price's exit was the biggest shock as he was the second highest-ranked player remaining in his half of the draw and was playing an opponent competing in his first PDC World Championship.
The Welshman tweeted afterwards: "Oh well what a night. Well done Nathan you done well, all the best to everyone left in the tournament."
Price was involved in an ill-tempered match with two-time world champion Gary Anderson in last month's Grand Slam final in Wolverhampton which led to both players being referred to the Darts Regulatory Authority after they squared up to each other.
The BBC reported that players could face punishments during matches in an effort to deter gamesmanship.
Aspinall, who averaged more than Price in every set bar the opener, will face Kyle Anderson in the third round.
"This is absolutely massive for me and my family, and I'm not done yet," he said afterwards.
"I know what I can do and I knew if I played my game I could win, even at 2-0 down I thought I would still win and I never gave up.
"Going full-time this year was a big risk for me and my family, but winning a ProTour event along with this win tonight gives me security and I couldn't be happier."
Like Price, White lost a two-set lead as South Africa's Devon Petersen moved into the third round and a meeting with Steve West.
The 32-year-old, who reached the last 16 in 2014, won 5-3 in the final set of a contest featuring 16 maximums.
Keegan Brown won a scrappy match with Klaasen, the 2006 BDO champion, 3-1.
Brown, who will play fellow Englishman James Wade in round three, had a modest three-dart average of 82.6 but ground down his Dutch opponent, who made only five of his 22 checkout attempts.
And to complete the night of surprises, world youth champion Dimitri van den Bergh beat Clayton 3-1 and will face Luke Humphries for a place in the last 16.
In the afternoon matches, Benito van de Pas survived a match dart before sealing a tie-break with Canadian Jim Long in style with a 150 finish.
Germany's Gabriel Clemens had a 10-dart leg but could not prevent defeat against Scotsman John Henderson, who secured a 3-2 win in a match of 13 maximums with a 120 finish.
West beat fellow Englishman Richard North 3-1, while Anderson saw off Noel Malicdem of the Philippines by the same margin.
Afternoon session (1230 GMT)
Ryan Joyce v Alan Norris
Dave Chisnall v Kim Huybrechts
Daryl Gurney v Jamie Lewis
Evening session (1900 GMT)
Ryan Searle v William O'Connor
Gary Anderson v Jermaine Wattimena
Michael van Gerwen v Max Hopp