Day 13 of the £2.5 million event saw the final 6 ties in the fourth round take place, with Saturday’s quarter-final line-up now confirmed following a dramatic conclusion to the night.
Humphries, a 500/1 shot at the start of the tournament, found himself two sets down to second seed Cross, who fired in three ton-plus finishes in an impressive start from the defending champion.
A determined Humphries regrouped, taking the third set 3-1 with a 115 finish before a trio of 15-dart legs saw the 23-year-old level the tie.
The fifth set also went the way of Humphries, as the Newbury man took the lead in sets for the first time in the match, before coming back from 2-0 down in the sixth set, reeling off three successive legs to book a quarter-final date with Michael Smith.
“I’m absolutely over the moon to knock out the World Champion on a stage he’s never lost on before,” said Humphries, who has topped the PDC Unicorn Development Tour Order of Merit in each of the last two years.
“When I went 2-0 down I said to myself ‘if you want to be World Champion you’ve got to dig deep’ and that’s what I did, I didn’t give up because you’ve got to fight back in those situations.
“Two years ago I might’ve given up there but I believe in my own ability and I’m hugely proud of myself for that performance tonight.
“I take a lot of inspiration from Rob and his win last year has given players like me the belief that I can win this, and if I keep showing resilience like this then I can go all the way.”
Smith cruised through to the quarter-finals for the second time in his career with a comfortable 4-1 win over Ryan Searle.
Smith took the opening set 3-1, and, after Searle went 2-0 up in the second, the Premier League finalist came back to double his lead with a 130 checkout.
Back-to-back 11-dart legs helped Smith on the way to a 3-0 lead, but after he missed two match darts in the fourth, Searle stepped in to take out double ten and reduce the deficit to 3-1.
Searle took the opening two legs of set five, but a dogged Smith came back once again with three successive legs, sealing the win with a 106 checkout.
Two-time World Champion Gary Anderson will meet Dave Chisnall in the last eight after the St Helens thrower made it back-to-back 4-0 wins as he defeated Jamie Lewis to reach the quarter-finals for the second time in three years.
Last year’s semi-finalist Lewis took a two-leg lead in the opening set, but Chisnall fought back to lead and followed that up by winning the second 3-1.
Set three went to a deciding leg, and after Lewis missed three darts to halve the deficit, Chisnall found the double to win the set at the ninth attempt, before sealing victory in the next to make it 11 consecutive sets in the tournament.
Ryan Joyce and Nathan Aspinall both continued their fairytale runs in their first Alexandra Palace appearances with victories to reach the last eight.
Joyce, who won his Tour Card in January, claimed the scalp of a seed for the third successive match as he overcame James Wade 4-3, following up his earlier defeats of Anastasia Dobromyslova, Simon Whitlock and Alan Norris.
Joyce landed a 138 finish to take the opening set before Wade took the next two sets to lead 2-1.
The fourth and fifth sets both went on throw to give Wade a 3-2 lead, but after he missed five darts for the match, Joyce stepped in to take the contest to a tense deciding set.
After Wade took the opening leg, Joyce responded with a 110 checkout followed by a break of throw to go within a leg of victory, and at the fifth attempt, the Geordie found the winning double to set up a clash with Michael van Gerwen.
The opening game of the day saw Aspinall – another player who claimed his Tour Card at Qualifying School in January – come back from 2-0 down to defeat Devon Petersen 4-3 in a roller-coaster affair.
African Qualifier Petersen raced into a two-set lead, but after missing three darts to make it 3-0, Aspinall turned the match on its head to take a 3-2 lead.
Petersen responded to take the tie to a deciding set which went to a tie-break at 2-2, before Aspinall held throw and then found a 13-dart break to book his place in the last eight.
Brendan Dolan reached the quarter-finals for the first time with a comfortable 4-1 victory over Benito van de Pas.
The Northern Irishman won nine of the opening 11 legs as he raced into a three-set lead before Van de Pas registered his first set.
However, it was to be Dolan’s day as the former World Grand Prix finalist edged the fifth set 3-2 to claim a resounding win.
Saturday will see the four quarter-finals take place across two sessions, with Aspinall v Dolan and Chisnall v Anderson in the afternoon, followed by Humphries v Smith and Van Gerwen v Joyce in the evening.
World number one Van Gerwen is now the 4/6 odds-on favourite with sponsors William Hill as he aims for his third World Championship title, with Anderson the 7/2 second favourite.
Smith is priced at 9/2 to pick up his maiden World Championship win, with Humphries 22/1, Chisnall 25/1, Aspinall 33/1, Dolan 50/1 and Joyce 100/1 to claim the title on New Year’s Day.
2018/2019 William Hill World Darts Championship
Schedule of Play
Friday December 28
Fourth Round x3
Nathan Aspinall 4-3 Devon Petersen
Brendan Dolan 4-1 Benito van de Pas
Ryan Joyce 4-3 James Wade
Fourth Round x3
Michael Smith 4-1 Ryan Searle
Dave Chisnall 4-0 Jamie Lewis
Luke Humphries 4-2 Rob Cross
Saturday December 29
Afternoon Session (1230)
Nathan Aspinall v Brendan Dolan
Dave Chisnall v Gary Anderson
Evening Session (1900)
Luke Humphries v Michael Smith
Michael van Gerwen v Ryan Joyce
Sunday December 30 (1900)
Tuesday January 1 (2000)