Luca Brecel failed to convert two match-winning chances before losing 6-5 to Shaun Murphy in the UK Championship quarter-finals.
Competing in the last eight of a ranking event for the first time, Brecel led 5-4 but missed a pink that should have seen him go on to victory.
Murphy will play Ali Carter, who beat Stuart Bingham 6-4, in the semis.
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Mark Davis beat Matthew Stevens 6-4 while Mark Selby came back from 4-0 to defeat Neil Robertson 6-4.
Brecel, who won four qualifying matches to reach the televised stages, was the only player from outside the world's top 16 in the quarter-finals.
The world number 74 made a confident start with breaks of 39 and 41 to take the opener, but Murphy edged a tight second frame before a fluent 122 put the Englishman 2-1 up.
Brecel levelled it at the interval and there was never more than a frame in it, Murphy nudging ahead again before breaks of 46 and 31 from Brecel made it 3-3.
He was on course to take the next with a break of 48 to the colours before going out of position on the last red and missing a difficult blue.
But Murphy missed a green to let him back in and Brecel, who earlier this year became the youngest to play at the World Championship at the Crucible, went ahead for the first time since the opening frame at 4-3.
The world number four drew level with a run of 79, but Brecel stayed composed, rattling in a 64 - his highest break of the match - to move within one frame of victory.
A nervy 10th frame came down to the final two balls and Brecel had a chance to wrap up victory, but missed the pink to allow Murphy to take it to a decider.
Brecel led 30-12 in the final frame but Murphy made 42 before getting a kick on the the final red. The 17-year-old cleared to the blue but left himself a difficult long pink, rattling the jaws to let a relieved Murphy in.
"The kid didn't seem to feel any pressure until the end," Murphy told BBC Sport. "I thought I was out two or three times to be honest. Maybe I have played my get-out-of-jail card.
"I have been in his position. He might look as if he wasn't nervous, but I am sure he was feeling it inside. But what a great week he has had."