Luke Littler hit a spectacular nine-darter as he overcame Josh Rock 17-14 to set up a World Matchplay final against James Wade on Sunday.
The 18-year-old world champion was trailing 6-1 before completing the feat to deny Rock – who had hit two 180s – the chance to do so himself.
With 15 perfect darts, it can lay claim to be the greatest leg in the history of the tournament.
"It definitely sparked me into life. I didn't want to give it big because I was playing awfully," said Littler.
His fellow Englishman Wade, 42, reached his seventh Matchplay final with a 20-18 win over Wales' Jonny Clayton in an epic encounter on a thrilling night at Blackpool's Winter Gardens.
The teenager will aim on Sunday to become only the fifth player to win the Triple Crown, after Phil Taylor, Michael van Gerwen, Gary Anderson and Luke Humphries.
Littler is looking to seal the treble in little more than a year, eyeing Matchplay glory having won the Premier League in May 2024 before his World Championship triumph in January.
"I've won many finals and majors but this is the big one now, it all comes down to Sunday," he said.
It will be a repeat of the UK Open final in March, which Littler won 11-2.
That prospect looked unlikely as 24-year-old Rock, a World Cup winner with Northern Ireland, came out firing and opened up a 5-0 lead in the first session.
But then came Littler's brilliant nine-darter, which evoked memories of darts' greatest leg when Michael Smith did the same in the 2023 World Championship final after Van Gerwen just missed with his ninth dart.
"That is the second-best leg you will ever see in your life," said Sky Sports pundit Wayne Mardle.
This was the 10th nine-darter at the tournament, which started in 1994, and the first this year.
It may have only been greeted with a shrug from Littler but it prompted him into a much-improved performance, and from 8-4 down he won seven of the next eight legs to go 11-9 in front.
Rock hit consecutive checkouts of 170 and 120 to close the gap to 14-12 but Littler prevailed in a match where he averaged 107.5 to his opponent's 104.15 and edged the 180 count 15-14. The maximums tally of 29 is a Matchplay record.
Earlier, Wade was one leg away from victory at 16-10 before Clayton reeled off six successive legs to force overtime.
"I'm just done, I'm exhausted. I hope the crowd here and everyone at home enjoyed themselves, because I hated every minute of it," said Wade.