Judd Trump saw his hopes of defending the williamhill.com UK Championship title shattered by a first-round exit to Mark Joyce.
The world number one led 5-2 and was seemingly heading for a comfortable win in the best-of-11 contest, but Walsall journeyman Joyce produced a great fightback to win 6-5.
Trump's concentration looked to slip and form certainly deserted him, with Joyce taking advantage to set up a second-round clash against World Championship runner-up Ali Carter.
Two years ago, Joyce also saw off Trump in the UK Championship, and Carter was another of his victims on his way to the quarter-finals, but he has failed to reproduce such form since, partly due to an arm injury.
Only last month Trump won the International Championship title, the most lucrative tournament China has ever staged, and he came to York's Barbican Centre as firm favourite to take another trophy.
But he confessed: "Nothing seemed to go right. I didn't play well - it's disappointing.
"I'd done well to go 5-2 in front but I didn't really have any clear-cut chances after that and my long-potting was just awful. You can't win them all."
Carter booked his place in the second round with a 6-2 victory over veteran Steve Davis.
Both men struggled for fluency, Carter's highest break of 88 and an 85 from Davis in the seventh frame out of keeping with the flow of the match.
Yet Carter was the more consistent of the two, with the 33-year-old from Tiptree too strong for the 55-year-old Brentwood veteran, making his 33rd appearance in the event.
There was a further shock in the late session when Marco Fu of Hong Kong saw off Mark Allen 6-3.
It was a disappointing loss for the world number eight against a man he only recently once again claimed had cheated in the past.
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