Michael Smith ended Gerwyn Price's reign as World Champion, winning 5-4 in an incredible quarter-final which saw Price hit a nine-darter.
Price was left to rue two missed match darts as Smith kept his composure to move one game away from a second World Championship final.
Smith will return for Sunday's semi-finals night to take on James Wade, who breezed past Mervyn King 5-0.
Former World Champions Peter Wright and Gary Anderson will meet in an all-Scottish tie after the duo enjoyed victories over Callan Rydz and Luke Humphries respectively as the quarter-finals took place across two sessions on New Year's Day.
Yet another incredible night of action saw Price hit his first televised nine-darter and the third of this year's tournament, setting a new World Championship record.
Despite hitting perfection in set four, Smith averaged 121.33 to win the set to level the contest at 2-2 before Price took the fifth set to regain the advantage at 3-2.
The following two sets were shared, with Price leading 4-3 heading into what proved to be a decisive eighth set.
After Price missed darts at double top and double ten for the match, Smith held his nerve on double eight to force a ninth set.
Smith broke throw in the first leg of the decider and backed it up with a 108 checkout to put Price on the ropes.
The world number one held throw to stay alive but missed tops for a 110 finish in what proved to be the final leg as Smith pinned double 12 for a memorable win.
"I'm so happy, this is up there with one of the best nights of my career," said Smith.
"I thought I played really well but I started shaking towards the end and I had to compose myself.
"When I was on the last double 12 I just said to myself 'focus on what you've been working on for the last 12 months'.
"I'm one step closer to living my dream. This is my chance."
An unforgettable start to the year also saw Wright defeat Rydz in a nine-set thriller to reach his fourth World Championship semi-final.
The 2020 champion recovered from 3-1 and 4-3 down to deny 23-year-old sensation Rydz the biggest win of his life.
A captivating contest saw Rydz get off to a dream start in his first quarter-final appearance, averaging 110 and pinning a 152 checkout to take the opening set.
Rydz continued to endear himself to the crowd, winning two of the next three sets as he took the game to his more experienced opponent.
Wright won the next set to reduce the deficit to 3-2, before a crucial sixth set saw him miss double 12 for a nine-darter, and after Rydz missed a dart at tops for the set, Wright hit double 18 and tops for a 96 checkout to make it 3-3.
Rydz refused to wilt, winning the next set 3-1 to regain the lead before Wright won the eighth set 3-0 to force a ninth and final set.
The decider saw Wright break in the first leg and hold throw to move within a leg of victory, only for Rydz to fight back once again, winning back-to-back legs to force a tie-break.
Wright then pinned a vital double nine with his last dart in hand to break throw once again and this time held throw to bring the curtain down on a classic.
"I'm happy with the win but I was annoyed with myself for missing crucial doubles throughout the match which let Callan back in," said Wright.
"That was why I reacted the way I did at the end, it was a release of frustration for not getting the job done earlier.
"It was a great match to play in, not many people would've beaten Callan the way he played tonight. I think my experience got me through in the end.
"I'm looking forward to playing Gary, I want to achieve as much as him before I retire.
"Hopefully the game will be as good as tonight's if not better."
Anderson continued his quest for a third World Championship title with a ruthless 5-2 defeat of Humphries.
A pulsating contest saw Anderson land four ton-plus checkouts as he reached the semi-finals for the seventh time.
Rising star Humphries made a perfect start to his third quarter-final appearance in four years as he took the opening set 3-0.
The next two sets went Anderson's way, before Humphries hit back to restore parity at 2-2.
Set five proved pivotal as Anderson recovered from 2-0 down, landing a 110 finish to break throw to win the set decider, before kicking off set six with a 148 checkout under pressure.
Humphries continued to apply pressure, but Anderson's experience showed as he kept cool to win each of the last three sets 3-2.
"I played alright but I missed a lot of doubles at the start," said Anderson, who hit four ton-plus checkouts.
"I've got not expectations whatsoever of winning this tournament; I just play my game and if it's good enough then great, if not I'll say good luck to the player who beat me.
"I'm not at my best yet but I feel like it's getting closer with each game."
Wade cruised into his third World Championship semi-final, his first in nine years, with a 5-0 demolition of King.
Wade displayed his trademark timing, winning three of the sets 3-2, to make it back-to-back whitewashes having beaten Martijn Kleermaker 4-0 in the fourth round.
King led 2-1 in both the first two sets, but was unable to recover from those setbacks as Wade cantered to the finish line.
"It wasn't expected, I thought I had a real battle on hay hands with Mervyn," said Wade.
"I was fortunate that Mervyn didn't play his game and I got away with a lot.
"Merv's beaten me so many times in a row prior to this but I've bashed him here and done a proper job on him.
"This is the first year I've had no chaos going on away from darts and I feel relaxed heading into the next round."
The world's biggest darts tournament returns on Sunday with the semi-final action starting at 1930 GMT.
The tournament is being broadcast live on Sky Sports in the UK, through the PDC's worldwide broadcast partners including DAZN and RTL7, and on PDCTV (excluding UK and Netherlands based subscribers).
2021/22 William Hill World Darts Championship
Schedule of Play
Saturday January 1
Afternoon Session (1230 GMT)
James Wade 5-0 Mervyn King (3-2, 3-2, 3-1, 3-2, 3-1)
Gary Anderson 5-2 Luke Humphries (0-3, 3-2, 3-1, 1-3, 3-2, 3-2, 3-2)
Evening Session (1930 GMT)
Peter Wright 5-4 Callan Rydz (0-3, 2-3, 3-1, 1-3, 3-1, 3-2, 1-3, 3-0, 4-2)
Michael Smith 5-4 Gerwyn Price (2-3, 3-0, 2-3, 3-1, 1-3, 3-0, 2-3, 3-2, 3-1)
Sunday January 2 (1930 GMT)
Michael Smith v James Wade
Peter Wright v Gary Anderson
Best of 11 sets
(A tie-break rule is employed in all matches; where a deciding set must be won by two clear legs. If the score in the final set reaches 5-5 then a sudden-death leg will be played. There would be no throw for the bull in any sudden-death legs.)
Monday January 3 (2000 GMT)
Smith/Wade v Wright/Anderson