John Higgins overcame his great rival Ronnie O'Sullivan 13-10 in the World Championship quarter-finals to book a semi-final with Mark Williams.
O'Sullivan led 7-4 at one stage but the Scot won the last three frames of the second session to level matters at 8-8.
He won the first on the resumption before O'Sullivan knocked in 116, but Higgins proved the more consistent.
He won three frames in a row before O'Sullivan rallied with 94, but a fluke allowed Higgins to seal it with 79.
Attempting to play a safety shot from the bottom cushion, the three-time champion enjoyed a fortuitous plant on a red into the middle pocket, and took full advantage of his good fortune.
It was an unfortunate way for O'Sullivan - also a three-time Crucible champion - to ultimately lose, but he wasted several opportunities in the final session when well placed.
"At 8-5 down I thought I was on my way out of the tournament because Ronnie's the best front-runner we've got," the 35-year-old Higgins said.
"You can forget it sometimes. So it was lucky for me he missed a few he wouldn't normally miss.
"I don't know how I got back to 8-8. To say I was delighted would be an understatement. I felt I couldn't play any worse, and I couldn't afford to tonight, and I decided to be really positive and it worked out."
A poor attempt at a snooker on the final red cost O'Sullivan the first frame of the evening, but a brilliant long red along a cushion launched a break of 116 to make it 9-9.
Neither player consistently reached the heights of which they are capable, and Higgins - chasing a third title in five years, and fourth overall - capitalised on several errors with runs of 63, 65 and 73 to move within one frame of victory.
'The Rocket' responded with a fine 94 after Higgins missed a tricky pink to take the next, but the Scot closed out the match in style after his stroke of luck to record his fifth win in his last six ranking-event meetings with O'Sullivan since 2008.
O'Sullivan, who made the quarter-finals on the back of four first-round defeats in major events, conceded Higgins was a worthy victor, despite both missing a number of easy chances.
"I made far too many elementary mistakes which is unforgivable at this level, or any level, even amateur level," the 35-year-old said.
"I can't sit here and say I deserved to win because I don't think I did. I think I did well to get 10 frames."
It was only three weeks ago that O'Sullivan changed his mind after initially withdrawing from the tournament, claiming he was lacking motivation.
However, after linking up with sports psychiatrist Dr Steve Peters and delivering a reasonable showing at The Crucible, he is more optimistic about his future prospects.
"It was still sub-standard snooker, but I wasn't smashing myself to pieces out there," he added. "I'm in a better place, I feel happier, I feel better about life.
"It's not the playing that was hard for me, it was the in-between bits, the thinking and pondering about playing. I know it's not going to improve my game but if I can feel better about playing rubbish then I might hang around.
"I still want to play well. It's a work-in-progress thing, and if it means thinking great but playing like that, that isn't good enough for me. But I'll be patient with it."
It was a relieved Higgins who secured a semi-final date with in-form Welshman Williams, who comfortably disposed of Mark Allen 13-5 in his quarter-final.
Higgins has lost both their previous encounters at the Crucible, 17-10 in the 1999 semi-finals, and 17-15 at the same stage a year later, when Williams went on to win the first of his two world crowns.
"Playing Williams now will be a very tough game. He's beaten me twice before in semi-finals here, and he's back to playing the way we all know he can play," Higgins said.
"That'll be just like a final because there's only one less frame than the World Championship final, and it's something to look forward to."