Mark Williams claimed his first victory over Ronnie O'Sullivan in a ranking event for 12 years at the International Championship in China.
The Welshman had lost eight consecutive ranking matches against O'Sullivan but he recovered from a 3-0 deficit in Chengdu to win 6-5 and set up a semi-final with Mark Allen on Saturday.
Two-time world champion Williams, 39, is chasing his first ranking title since the 2011 German Masters and breaks of 120, 59 and 77 gave him momentum and helped him to five frames in a row before O'Sullivan fought back to set up a decider.
Williams had first chance and made 50 before running out of position. O'Sullivan cross-doubled a red to give himself a chance to counter, but then missed a tricky black and Williams doubled a red himself before adding 22 to seal the result.
"I haven't beaten him for so long, eventually I've got rid of that pain," world number 22 Williams told worldsnooker.com.
"I was shocking for the first few frames and dragged Ronnie down, but after the interval I was a different player.
"It's an excellent win for me, even though Ronnie wasn't at his best. He's still the best player in the world."
Five-time world champion O'Sullivan, who is yet to win a title this season, said: "We both started poorly and I was struggling with my concentration.
"Then he played well to go 5-3. He's in good touch. At 5-3 I felt I had to make something happen, and that was the best I felt in the match."
Allen also had to come from behind as he overturned a 3-1 deficit to beat Michael White 6-3, the Ulsterman reeling off five frames in a row with top breaks of 84, 76, 58 and 58.
"Even at 3-1 down I felt that if I played well I would go on to win, and I did that after the interval," said world number eight Allen, who is targeting his fourth final of the season having won the Paul Hunter Classic and finished runner-up at the Riga Open and Shanghai Masters.
"I've been practising hard this season and I'm getting results."
Robert Milkins will play Ricky Walden in Friday's semi-final, the former edging past Marco Fu 6-5 in a high quality contest to reach the fifth ranking semi-final of his career.
Gloucester potter Milkins won the deciding frame against Fu with a clinical 70 finish, while Walden, who has won both of his two previous world ranking titles in China, cruised into the last four with three centuries in a 6-1 defeat of Jamie Burnett.
The winner of the title on Sunday will receive £125,000, the biggest prize on offer in snooker outside the UK.