Barry Hawkins shocked world number one Mark Selby 13-10 to reach the quarter-finals of the World Championship for the first time.
Selby resumed 9-7 up but Kent-based Hawkins, 34, ground out winning frames to repeat last year's win over Selby.
Meanwhile, Judd Trump defeated Marco Fu 13-7 to reach the last-eight.
Australian Open winner Hawkins, who advances past the second round for the first time in eight attempts, built a highest break of 89 and it was his combative game which left Selby unable to gather any momentum.
"I struggled all the way through the match and Barry took the chances and scored better than me," admitted Selby.
"I have struggled all season but won two events, even though I was not playing great.
"Coming here I was confident but to perform like that is a disappointment. I had no drive, no buzz out there and I didn't really show up."
Despite falling 9-7 behind, Dartford cueman Hawkins battled back by winning the 17th frame on the black - and it proved to be the turning point.
Selby, who usurped Trump at the top of the rankings after finishing second in the China Open, missed opportunities in that frame to increase his advantage further and Hawkins levelled the scores in the next.
The pair exchanged frames for 10-10, before Hawkins punished his opponent for uncharacteristic misses by winning the next two frames.
It left him one away from causing a huge upset and the world number 14 showed no signs of Crucible jitters to set up a tie against either Mark King or Ding Junhui in the last eight.
"I am lost for words - I am just delighted," said Hawkins. "It is one of the best results of my life - I feel like I have won the World Championship.
"Everybody left in the tournament has to feel they can win it otherwise there is no point in turning up. If I can find some fluent form, you never know what might happen."
Earlier on Saturday, England's Trump opened up a 6-2 lead against Marco Fu in the first session, stroking in three century breaks on his way to establishing a commanding lead.
But breaks of 83, 117, 66 and 70 saw Hong Kong's Fu reduce his deficit to 8-7 before the world number three won the last to edge ahead.
Trump, runner-up in 2011, started the final session in blistering fashion, knocking in quick-fire breaks of 50, 82 and 53 to go one away from victory, and despite being 53 behind, he pinched it on the black to set up a meeting with 2005 champion Shaun Murphy in the next round.
"It was nice to get it over and done with. I struggled earlier but I am pleased to get through," said Trump.
"Coming into the tournament, I felt the ones who hadn't played too much would go on and those who had, would burn themselves out, which is what has happened.
"I felt fresh and fit going into the second session of the day and I will be prepared for Shaun."
World number 17 Fu added: "I felt OK but I missed one or two shots and lost my way. I didn't play that badly, but Judd punished me. It was costly against the calibre of someone like him. There is no reason why he can't go on to win it."