Underdogs storm into semi-finals as Cross shocked at Grand Slam of Darts
Lukeman stunned world number four Rob Cross with a 16-11 victory, while Mansell edged out Cameron Menzies 16-15 in a thrilling encounter.
Cross, the 2022 runner-up, raced into an early lead but Lukeman fought back with a series of clinical finishes, including a stunning 144 checkout.
Despite a late rally from Cross, who clawed it back to 10-10, Lukeman held his nerve to secure a historic win in Wolverhampton.
"It's absolutely brilliant but I've got two more to go," Lukeman told the PDC website.
"I've been dreaming of winning the title since the group stages.
"I fear no one; I've beaten all the big players before so why not here?
"I've been practising a lot over the last few months, and it's showing on the big stage.
"I've always been a slow starter, and I knew I had plenty of time to come back into it, so I didn't panic.
"Mickey is a gentleman and a good player, but I'm up for a war on Sunday."
Mansell makes it
Mansell, a veteran of the sport, produced a heroic performance to overcome Menzies in a marathon 31-leg match.
The pair traded blows throughout the contest, with Menzies, a Players Championship event winner in October, racing into a 4-0 lead before Mansell won eight of the next 12 legs to level at 8-8.
After more back-and-forth, Mansell eventually prevailed in a tense deciding leg after taking out 59 via tops in a single attempt to claim the biggest victory of his career in his first-ever televised quarter-final.
"It's an unbelievable feeling," said an emotional Mansell after the victory. "I've put in so many hours of practice over the years for this moment.
"Not many people get these opportunities, and tonight was an opportunity I couldn't let pass.
"My scoring was fantastic tonight. I felt I was the better player, but I was just missing too many doubles.
"All of a sudden, the doubles left me, but I stuck in there, and tops came good for me in the end.
"I've probably never felt nerves like I did in the last leg but I've been in the same situation against Brendan Dolan at the World Championship; I lost on that occasion but I learnt from it."
The remaining quarter-finals will be played on Saturday, with Luke Littler facing Jermaine Wattimena and Gary Anderson taking on Gian van Veen.
