Defending champion Ronnie O'Sullivan said he felt "awful" after he overcame talented Chinese teenager Luo Honghao 5-3 to reach the semi-finals of the English Open in controversial circumstances.
O'Sullivan went 2-0 up after runs of 118 and 90 but 18-year-old left-hander Luo won three in succession, taking the lead with a superb break of 136.
However the five-time world champion, 42, enjoyed some luck when a foul he accidentally committed in the sixth frame went unnoticed.
He brushed a red with his cue after potting a different red with the rest.
After the match O'Sullivan realised what had happened when showed a TV replay.
"I didn't even see that in a million years," he said. "I'm happy to go play the match again if they want to. I feel awful after you showed me that.
"I wish someone would have said something and stopped the match - that's what they should do."
O'Sullivan's win secured a semi-final against Mark Davis, who beat Ryan Day 5-1.
Stuart Bingham will play Stephen Maguire in the other semi-final.
O'Sullivan capitalised on his young opponent's early nerves to go ahead with his 957th career century break but Luo went 3-2 up with a superb century clearance of his own, nonchalantly knocking in the final black right-handed.
After 43 minutes without potting a ball, O'Sullivan levelled at 3-3 with a 73 when his inadvertent brush with the red was not detected.
In the next, Luo, who chose snooker over a potential career as a concert pianist, rattled in a 56 all with reds and blacks but missed a red with the rest and O'Sullivan moved ahead again with a masterful 82.
A run of 41 was enough to take O'Sullivan through but he told Eurosport: "I can't believe I won that match - I was so much the second best. This is his first year on tour. If that's what he's like now, what's he going to be like in two or three years? He's going to be the best."
In the other matches Bingham made a 138 in the opening frame to beat Ali Carter, while 46-year-old Davis, yet to win a ranking event, reached his sixth semi-final and Maguire made a century en route to a 5-3 win over Thailand's Noppon Saengkham.
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