Defending champion Luca Brecel fell foul of the Crucible Curse as he somehow lost 10-9 to David Gilbert in a match he had dominated for most of the opening day.
Brecel had never previously won a match in Sheffield prior to last year's stunning victory, which saw him oust Ronnie O'Sullivan before seeing off Mark Selby in the final.
Returning now with another historical trend to overcome, the so-called 'Curse', Brecel made a breezy start and the prospect of him falling at the first hurdle only began to emerge late into the evening.
Leading 9-6 after a fluked red had seemingly helped him to shake off Gilbert for the final time, Brecel surrendered a good chance in frame 16 before Gilbert got within one, and then the Belgian missed a simple green to allow Gilbert to force a decider.
For the first time in the match, Gilbert was able to take control when the snooker he laid opened up a frame and match-winning opportunity, but just as he appeared set to complete the job he missed what would've been the final required red.
Brecel came to the table trailing 69-0 with 75 points available but a sloppy safety shot left Gilbert with a second bite of the cherry, and this time he made no mistake with an excellent red to the centre pocket.
Gilbert could only play safe from the following colour, but Brecel had one final surprise left in his reign, conceding the match with just one snooker required. It was the most peculiar end to a game he should have won.
Brecel told Eurosport: "Yeah, (I'm) tired. It was not easy being ill, but I tried. Dave played well, he's a fantastic player. He deserved it. He's a good guy, I hope he wins it.
"I never really settled, never really felt good. I played some good stuff in patches but I was really tired, the last session was difficult.
"It's not an excuse, it is what it is. Everyone gets ill sometimes. It was a good match.
"He's such a lovely guy. I hope he does really well."
Gilbert said: "I'm over the moon. The state of my game, literally four or five weeks ago... I've got to thank Andy Lee. He came and stayed with me the last four weeks and we've practised every day, or been in the gym.
"It was absolutely a great decision we made so I just want to thank Andy for getting me to hit balls again.
"To beat the world champion, who I have massive respect for, yeah I'm over the moon."
Also on the opening day, Judd Trump took control of his match with Hossein Vafaei, leading 6-3, while Tom Ford established a similar 6-3 lead over Ricky Walden.
Jak Jones and Zhang Anda were only able to complete seven frames of their match, with the former holding a 5-2 lead, while Ali Carter leads 5-4 against Stephen Maguire.
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