Stephen Maguire fought back from 5-1 behind to beat Neil Robertson 6-5 in the opening round of the Masters.
Australian Robertson, 37, a Masters winner in 2012, made breaks of 76, 136, 71 and 45 on his way into a 5-1 lead.
Maguire, 38, recovered with a break of 105 in the seventh, came from 56-0 and 40-5 behind to win the next two frames and then made a clearance of 81.
Robertson held a 33-point lead in the deciding frame but Maguire's break of 62 saw him dramatically win the game.
He will play England's David Gilbert after the 38-year-old, on his Masters debut, thrashed Northern Ireland's Mark Allen 6-1 in the second match on Monday.
Breaks of 77, 121 and 58 helped Gilbert into a 4-0 lead, before Allen, who won this event two years ago, edged a tight fifth frame.
But Gilbert, a World Championship semi-finalist in April, then made breaks of 95 and 53 to seal his place in the quarter-finals, while Allen only made one half century break in the match - an effort of 51 in the third frame.
'I had it in my hands'
Scotland's Maguire, who punched the air when he sealed his victory, said he was surprised he was able to win the last five frames against Robertson.
"It was a crazy game and I can't believe I won that match," said Maguire.
"He was the much better player all the way through the match and he should've put me to bed 6-0 or 6-1. He should've killed me but I could see the game turning.
"I've only come back from 4-0 down a couple of times in my career."
Robertson, the 2010 world champion, looked on course for the next round when 5-2 and 56-0 ahead but he missed a green, before he wasted a 35-point advantage in the next frame.
"There was a lot of rustiness and I've not played competitively for about a month," said Robertson.
"He deserved to win and I have no complaints, it's just unfortunate to go out of the Masters when I had it in my hands."
The tournament at London's Alexandra Palace features the top 16 players in the world, although five-time world champion Ronnie O'Sullivan opted to miss the event.
His replacement, Ali Carter, 17th in the world rankings, beat former world number one Mark Selby, with England's Joe Perry also defeating China's Ding Junhui on Sunday.
Last week, Robertson, who comes from Melbourne, announced he would be making a donation to the victims of the Australian wildfires.
Robertson has said he will pay £100 per century break made by any player during the Masters as well as an additional £5,000 to the New South Wales wildlife charity Wires, which rescues and cares for stricken animals.
World Snooker Tour then announced it would match the payment.