Stephen Lee beat defending champion Ronnie O'Sullivan 5-4 in a gruelling European Open quarter-final in Malta.
Lee claimed his first win over O'Sullivan in a ranking event
O'Sullivan rallied from 3-2 down to lead 4-3 before a 59 break saw Lee level the match.
Former world champion O'Sullivan then led 36-0 in the decider before Lee responded with 46 and fluked a snooker to win in three hours, 32 minutes.
Lee was joined in the last four by Jimmy White, who beat Australian Neil Robertson 5-3.
"That was very, very poor," said O'Sullivan, after his defeat. "It was like pulling teeth and it wasn't like me."
He added: "I can't believe what I've done lately considering the way I've been
"In the last two tournaments I've played one good session of snooker. That's it.
"I like to win Ronnie style, not just hang in there, so it's been too much like hard work. I've toughed it out but that's not the way I like to play the game."
Lee said: "Every time I've played Ronnie in the past he's been outstanding but today he
"I'm hitting the ball all right. It's just a matter of fine tuning. I'm quietly confident."
White qualified for his third major semi-final of the season after a 5-3 win over Robertson.
White moved into a convincing 4-1 lead before the Australian battled back to win the next two frames.
Robertson's nerves, though, buckled in the eighth, while White clearly took his first chance to seal the win.
"I'm playing well but I was tired after beating Stephen," said White, who defeated Stephen Hendry in the previous round.
"I was cruising at 3-1 and nicked a frame to go 4-1 up but then I lost a bit of composure and all of a sudden he looked a lot stronger.
"It was looking like 4-4 all over the place but I potted a fantastic long red in the last to win it."
White will play Tony Drago in the last four after he swept aside Australian Quentin Hann 5-1.
The Maltese player quickly wrapped up the first four frames, conceding only the fifth frame to Hann, before sealing the win in front of his home crowd.
"Today was the best I've felt in the arena for a long time," said Drago.
"I have such great support here and it lifts me. They are all hungry for me to win a trophy."
Lee, meanwhile, faces Stephen Maguire in the semi-finals after the Scottish 22-year-old upset countryman John Higgins 5-3 to reach his first ranking semi-final.
Higgins, the world number four, took the opening two frames but then lost the next four as Maguire took control.
"I'm starting to think about winning it now," said Maguire.
Higgins said: "I started okay but I missed so many chances in the third frame and that was crucial."