Defending Welsh Open champion Mark Selby was knocked out in the first round by China's Jiang Jun on Monday, losing 4-3.
The two-time Welsh Open winner took a commanding 3-1 lead with breaks of 123 and 137 at Venue Cymru in Llandudno.
But on his first appearance in the main draw of the competition, Jiang rattled off three consecutive frames to cause a huge upset on day one.
The 20-year-old had half-century breaks of 52 and 65 as he fought his way back to book a place in the second round.
It is the third time in five years that Englishman Selby, a four-time world champion, has been knocked out in the first round of the Welsh Open.
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It was an excellent first day for the Welsh players, as Jak Jones, Dylan Emery and Mark Williams all won their first-round matches.
Jones took a comfortable 4-1 win over England's Liam Highfield, while Emery shocked China's Lei Peifan with a deciding-frame victory.
Home favourite Williams - who was the last Welsh player to win the title back in 1999 - overcame Michael Holt to win 4-2 and set up a second-round match against Martin O'Donnell or Tom Ford.
England's Robbie Williams knocked out world number 16 Si Jiahui with a 4-2 win.
Williams will face last year's runner-up and former Welsh Open winner Stephen Maguire in the second round after his come-from-behind win over Ricky Walden.
Barry Hawkins was forced to go the distance against fellow Englishman David Lilley, though the 12th seed came out on top with a 4-3 win, sealing his win with a 108 break in the decider.
Welsh Open day one
Morning and afternoon results:
- Jak Jones 4-1 Liam Highfield
- Lei Peifan 3-4 Dylan Emery
- Pang Junxu 4-2 Antoni Kowalski
- Mark Williams 4-2 Michael Holt
- Yuan Sijun 4-3 Julien Leclercq
- Si Jiahui 2-4 Robbie Williams
- Barry Hawkins 4-3 David Lilley
- Hossein Vafaei 4-1 Artemijs Zizins
- Mark Selby 3-4 Jiang Jun
- Stephen Maguire 4-3 Ricky Walden
Evening schedule:
- Tom Ford v Martin O'Donnell
- Joe O'Connor v Aaron Hill
- Neil Robertson v Michal Szubarczyk
- Wu Yize v Ben Mertens
- Mark Allen v David Grace
- Ali Carter v Anthony McGill