World number 51 Jamie Jones stunned former champion Shaun Murphy with a 10-9 victory at the Crucible.
Welshman Jones dumped the 2005 winner out of the Betfred World Championship, holding his nerve to seal the deciding frame 72-1.
The 30-year-old turned the tide late on Monday afternoon with a superlative 124 break in the penultimate frame to take the match the distance.
Then the Neath native kept it together to ensure he despatched the current world number eight, booking a second-round clash with Kyren Wilson.
Jones rallied from 8-5 down to complete a remarkable comeback, adding another impressive scalp, having already beaten Liang Wenbo 10-0 in qualifying.
Mark Allen saw off Crucible debutant Liam Highfield 10-5 to move into the second round.
The Masters champion turned his 6-3 overnight lead into a relatively straightforward victory, even though Highfield produced a 99 break in Monday's first frame.
Allen then rattled through the next three frames, including a seventh half-century break as he secured the win.
The 32-year-old will now meet Joe Perry in the second round, after the world number 22 pulled off a shock victory over defending champion Mark Selby.
"I didn't score as heavily as I would have liked but I did enough to win," Allen told the BBC.
"It was a good match even though it was not the most free-flowing. Liam pushed me all the way and there were lots of close frames."
Highfield admitted a missed brown in the second frame of the day on Monday proved the turning point in his defeat.
"The brown was really tough and, had that gone in, then maybe it would have been 6-5 and a different match," Highfield told the BBC.
Barry Hawkins beat Stuart Carrington 10-7 to reach the second round, emerging victorious in an evening session that stretched almost until midnight.
Ding Junhui built up a 6-3 lead over Xiao Guodong, with Ricky Walden moving ahead 6-3 against Luca Brecel.