Ding Junhui crashed out of the UK Championship at the first hurdle as he blew a 5-1 lead against world number 130 Leo Fernandez in York.
World number three Ding has been suffering with an eye problem which has seen him miss the recent Shanghai Masters and Northern Ireland Open.
But despite losing the first fame to Ireland's 41-year-old Fernandez - a 12/1 pre-match chance with Sky Bet - the two-time tournament winner looked to be in command of their first-round match when he opened up a 5-1 advantage thanks to breaks of 60, 55, 90, 91, 66 and 87.
However, Limerick-born Fernandez - a former English Amateur champion - refused to be beaten even at 100/1 in-running and clawed his way to force a decider which he won by potting the pink and black to claim a famous victory.
"It’s my best moment in snooker for sure," Fernandez - who has never been beyond the last 16 of a ranking event - told worldsnooker.com.
“At 5-1 down I was thinking about the train journey home. I tried to stay calm and enjoy it.
"I’m suffering from a slipped disc in my back and sciatica so I’m lucky to be here. It was hard fighting the pain. The adrenaline kept me going and I started to play well.
"I’m having physiotherapy and acupuncture. I might need to have surgery which could end my career, but if that happens at least I’ll take this win with me.”
Fernandez had not won a match in four tournaments since returning from a 15-month ban after admitting playing a foul shot to facilitate a betting sting in a World Championship qualifier last year.
Elliot Slessor was brought back down to earth after his run to the semi-finals of the Northern Ireland Open last week as he was beaten 6-5 by Thepchaiya Un-Nooh.
Gateshead's Slessor raced into a 3-0 lead but Un-Nooh hit back to go 5-3 ahead thanks to runs of 82, 90, 81 and 53. Slessor won the next two, knocking in a 66 to force the decider which Thailand's Un-Nooh claimed thanks to a clearance of 99.
Welshman Ryan Day had breaks of 90, 110, 86, 122 and 83 as he whitewashed Jamie Curtis-Barrett 6-0, while Marco Fu saw off veteran Nigel Bond 6-2 which included runs of 83, 69, 89, 52 and 110.
Chinese teenager Yan Bingtao showed there was no hangover from Sunday's defeat to Mark Williams in the final of the Northern Ireland Open as he thrashed Zhang Yong 6-1 thanks to breaks of 78, 103, 60, 50, 68 and 61.
Three time UK champion John Higgins had few problems in seeing off Chris Totten 6-1 and world No 15 Kyren Wilson was just as clinical in seeing off Sean O'Sullivan by the same score with breaks of 108, 101, 96 and 52.
Tuesday's first-round results
- Ryan Day 6-0 Jamie Curtis-Barrett (Match 7)
- Thepchaiya Un-Nooh 6-5 Elliot Slessor (Match 8)
- Rory McLeod 5-6 Zhao Xintong (Match 15)
- Marco Fu 6-2 Nigel Bond (Match 16)
- Mike Dunn 6-2 Fang Xiongman (Match 25)
- Mark King 6-0 Boonyarit Keattikun (Match 26)
- Noppon Saengkham 6-2 Zhang Anda (Match 63)
- Ding Junhui 5-6 Leo Ferandez (Match 64)
- Kyren Wilson 6-1 Sean O'Sullivan (Match 21)
- Yu De Lu 6-2 Ian Preece (Match 22)
- Yan Bingtao 6-1 Zhang Yong (Match 29)
- Ben Woollaston 6-2 Lui Yuan (Match 30)
- Tian Pengfei 5-6 Cao Yupeng (Match 31)
- John Higgins 6-1 Chris Totten (Match 32)
- Stephen Maguire 6-1 Tuan SiJun (Match 39)
- David Grace 4-6 Jak Jones (Match 40)
WEDNESDAY NOVEMBER 29
Morning Session (0930 GMT)
First Round (Best of 11 frames)
Coverage: Eurosport Player
- Ricky Walden v Duane Jones (Match 23)
- Jamie Jones v Craig Steadman (Match 24)
- Sam Baird v Aditya Mehta (Match 27)
- Luca Brecel v Soheil Vahedi (Match 28)
- Mark Davis v Xu Si(Match 45)
- Zhou Yuelong v Peter Lines (Match 46)
- Hossein Vafaei v James Wattana (Match 59)
- Anthony McGill v Ashley Hugill (Match 60)
Afternoon Session (1230 GMT)
First Round (Best of 11 frames)
Coverage: Eurosport Player
- Peter Ebdon v Allan Taylor (Match 13)
- Anthony Hamilton v Lyu Haotian (Match 14)
- Shaun Murphy v Hamza Akbar (Match 17)
- Daniel Wells v Liam Highfield (Match 18)
- Jimmy Robertson v Alex Borg (Match 20)
- Judd Trump v Matthew Bolton (Match 33)
- Robbie Williams v Martin O'Donnell (Match 57)
- Martin Gould v Joe Swail (Match 58)
Evening Session (1930 GMT)
First Round (Best of 11 frames)
Coverage: Eurosport Player
- Mark Selby v Basem Eltahhan (Match 1)
- Scott Donaldson v John J Astley (Match 2)
- Jack Lisowski v Wang Yuchen (Match 41)
- Joe Perry v Billy Joe Castle (Match 42)
- Oliver Lines v Mei Xi Wen (Match 47)
- Mark Allen v Lukas Kleckers (Match 48)
- Michael White v Ross Muir (Match 51)
- Matthew Selt v Ian Burns (Match 52)