Defending champion Mark Selby insists he has no excuses after he made an early exit at the Betway UK Championship in York.
The world number one took a 2-0 lead against Scott Donaldson in the best-of-11 frame format but the three-time world champion lost six of the next seven to suffer a 6-3 second-round defeat.
Selby took the opening frame courtesy of a 68 break and extended his advantage before the 23-year-old halved the deficit with a wonderful run of 88.
Donaldson won the next two to nudge ahead for the first time in the match before Selby levelled following another half-century run.
The Scot maintained his composure and rattle off the last three frames to earn the shock win after compiling breaks of 90, 77 and 84 to advance to the third round of the competition for just the second time in his career.
Selby praised the young Scot, who will face China's Li Hang in the third round at the Barbican Centre.
He told worldsnooker.com: "Everyone seems to be playing at that standard against me at the moment. I rate Scott as a player, he's got a good all-round game, he scores well as you've just seen today.
"It didn't surprise me, him playing like that, because I've played him before four or five times and he's performed like that every time. He closed the match out really well.
"If I had kept missing and not taken my chances then it would have hurt a lot more. I've got no excuses."
The result is even more remarkable considering Donaldson had won just one match this season before the match, a 6-2 victory over John Astley in the first round in York, but the Scot held his nerve to claim the biggest victory of his career.
"In terms of the difficulty of my opponent it's my best win," Donaldson told worldsnooker.com.
"It has been well documented that I'd not won a game this season but I actually had a lot of cue problems.
"I have to say thanks to Raymond Cohen from Exquisite Cues because he has done a brilliant job with it, and I'll stop messing about with it now. I feel I'm back to where I was last year.
"I got good chances in the balls today and I capitalised on it. It doesn't always happen like that, on another day I wouldn't have had a look in. I took my chances and that's what you need to do in any game regardless of who you are playing."
Former champion Neil Robertson fired three successive century breaks as he cruised to a 6-2 victory over Ken Doherty.
The Australian moved 3-2 up with a run of 102 and followed it up with scores of 124 and 129 in the next two frames.
Judd Trump continued his flawless start to this year's tournament with a 6-0 second-round victory over Chris Wakelin.
The 2011 champion breezed past Matthew Bolton in the first round and he was at his ruthless best once again as he laid down a marker for the rest of competition.
The 28-year-old racked up two half-century breaks in the contest as he limited Wakelin to a highest run of just 38.
Marco Fu advanced to the third round with a rollercoaster 6-4 win against Zhao Xintong.
World number seven Fu never trailed in the match and began with a break of 86 in the opening frame before registering three more half-century runs en route to victory, despite Zhao remaining in touch throughout.
Stephen Maguire, the 2004 champion, eased to a 6-0 success against Jamie Jones, while Joe Perry defeated Jack Lisowski 6-3 win and Liang Wenbo secured a 6-1 success against Mitchell Mann.
Jimmy White, the 1992 winner, fell in the second round after suffering a 6-2 defeat at the hands of Kurt Maflin, while Peter Lines was a 6-2 victor against Xu Si and Graeme Dott won a final-frame shootout with Dominic Dale.
Mark Williams, who contemplated withdrawing from the competition after wife Jo was hospitalised, also won by the same scoreline against Andrew Higginson.
Mark Allen was a 6-4 victor against Oliver Lines and Ryan Day progressed to the third round with a 6-3 success over Thepchaiya Un-Nooh, while there were also wins for Mark Joyce and Lyu Haotian.
Click here for the full tournament schedule & results
SATURDAY DECEMBER 2
Afternoon Session
Second Round (Best of 11 frames)
Evening Session (1900 GMT)
Second Round (Best of 11 frames)
TV Coverage: BBC/Eurosport
SUNDAY DECEMBER 3
Afternoon Session (1300 GMT)
Second Round (Best of 11 frames)
TV Coverage: BBC/Eurosport
Evening Session (1900 GMT)
Second Round (Best of 11 frames)
TV Coverage: BBC/Eurosport