Belgian 17-year-old 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 the final pink in the 10th and 11th frames.
Murphy will play Ali Carter, who beat Stuart Bingham 6-4, in the semis.
Mark Davis beat Matthew Stevens 6-4 while Mark Selby came from 4-0 down to overcome 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."
Carter, twice a World Championship finalist including earlier this year, made breaks of 134 and 68 to establish a 3-1 interval lead over Bingham.
However, Bingham, the world number 11, made 47 to reduce his deficit before Carter re-established a two-frame advantage.
But Bingham drew level at 4-4 before a 60 saw Carter regain the initiative and take the next to seal victory.
Davis also reached the semi-finals after a 6-4 victory over the 2003 UK champion Stevens.
The 40-year-old fired breaks of 101, 80 and 70 to see off his Welsh opponent and continue the most successful season of his professional career spanning 21 years.
Having reached the semi-finals of a ranking event for the first time at this season's opening Wuxi Classic in China, and then repeated it at the next event, the Australia Open, Davis has made the last four for the third time.
"It's my first semi-final of the big ones in this country," he said.
"I don't know what's going on with my career. Getting in the top 16 for the first time at the age of 40 is probably some kind of record."
Davis will meet Selby on Saturday for a place in the final after the world number two saw off Australian Robertson in a late-night finish in York.
Selby, 29, had been facing elimination at 4-0 down but managed to claw his way back to 4-4.
The pair played cat and mouse in a nervous, 49-minute, ninth frame but once Selby had edged in front he wrapped up the victory in quick time with a smooth 101 break.