Defending champion Mark Selby crashed out of the UK Championship following a 6-3 second-round defeat to Scott Donaldson and afterwards insisted he had 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.
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."
Two-time champion Neil Robertson secured a comfortable 6-2 victory over Ken Doherty while 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.
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.
Marco Fu advanced to the third round with a rollercoaster 6-4 win against Zhao Xintong.
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.
Watch the Mosconi Cup live on Sky Sports between December 4-7. Coverage gets underway on Monday from 7pm on Sky Sports Action.