Defending champion Ronnie O’Sullivan blew a 3-0 lead to lose to Mark Davis in the Welsh Open second round.
World number 31 Davis looked to be heading out as O’Sullivan established a commanding lead in the best-of-seven contest.
Davis took the next four frames to complete a remarkable comeback on a day of shocks at the tournament.
Lee Walker pulled off a surprise as he came from 3-1 down to beat world number seven Neil Robertson 4-3.
Former world champion and 2016 finalist Robertson made 143 – the highest break of the tournament – on the way to a two-frame lead before Walker came back.
The Welshman, ranked 94, won the next three straight frames to seal victory.
Meanwhile, 15-year-old Welsh schoolboy Jackson Page reached the last 32 with a 4-3 win against John Astley.
It is the teenage amateur’s second win in the tournament after beating Jason Weston 3-1 in round one on Monday.
Page will now play the winner of the second round match between world number four Judd Trump and Alex Borg.
Elsewhere, Ross Muir thrashed Marco Fu 4-0 while Anthony Hamilton beat Jamie Cope 4-1 to set up a third-round tie against Craig Steadman, who defeated Sam Baird.
World Grand Prix finalist Ryan Day was knocked out by Thailand’s Thepchaiya Un-Nooh, who reached the third round of the tournament for the first time.
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