The 42-year-old O'Sullivan first won this event in 1993, aged 17, and he remains the man to beat. A 6-3 victory over Martin Gould including breaks of 107, 106 and 94 saw him safely through to the last four in York.
Maguire, who overcame Joe Perry 6-3 on the adjacent table, has met O'Sullivan in two previous UK Championship finals and a thriller could be in store when they go head to head again at the Barbican on Saturday afternoon.
When Maguire carried off the 2004 title at the age of 23, runner-up O'Sullivan tipped him as a player who could dominate snooker, but three years later the Rocket exacted revenge with a 10-2 saunter to glory.
Maguire has endured some challenging years since, landing just three more major trophies, while O'Sullivan has continued to pile up the big prizes and is chasing a 31st ranking title this weekend.
O'Sullivan said of the Glaswegian: "He's a great player, he's been around for a long time and is obviously hitting the ball well."
And looking back to Maguire's 2004 triumph, O'Sullivan said: "He smashed me up."
But he added: "It's ridiculous to look at what he said or what I said. I love him, he's a top guy. He could sit here and say I'm useless and that he's going to batter me, and I'd be like 'Sweet'. He could batter me and I'd still be his mate."
As ever, O'Sullivan will be backed by a partisan crowd on Saturday, but Maguire has no problem with being the underdog.
"I think it's harder for him," Maguire said. "They all shout for him and I wouldn't like to be in his position where you get 'Come on Ronnie' every single time he's at the table. It's not for me but he seems to handle it well."
Maguire remembered O'Sullivan's 2004 prediction that he could be in for a world-beating career.
"He does talk some b******s doesn't he," said Maguire. "Obviously that was a great win, I was up and coming then, playing well and fearless.
"He smashed me in the final in 2007. I'm not expecting an easy match but I'm looking forward to it.
"I hope it's a great match but I'm here to win and if I lose I'll be devastated. He's one of the only players I'd pay money to watch, the way he plays, and it's always a special occasion playing him. I think he's playing better now than he's ever done."
In the evening session, Shaun Murphy coasted into the semi-finals with a 6-1 win over Mark King.
Murphy opened up with a break of 71 before King, ranked at 21 in the world, levelled matters with a 53.
However, the world number six never looked like following several of the leading seeds out of the tournament as he then reeled off four successive half-century breaks to move 5-1 ahead before closing out a comfortable victory.
The other last-eight encounter took much longer to be decided as Ryan Day finally outlasted Mark Joyce 6-5 just after midnight.
FRIDAY DECEMBER 8
Afternoon Session (1300 GMT)
Quarter-Finals (Best of 11 frames)
TV Coverage: BBC/Eurosport
- Ronnie O'Sullivan 6-3 Martin Gould (QF 4)
- Stephen Maguire 6-3 Joe Perry (QF 3)
Evening Session (1900 GMT)
Quarter-Finals (Best of 11 frames)
TV Coverage: BBC/Eurosport
- Ryan Day 6-5 Mark Joyce (QF 1)
- Shaun Murphy 6-1 Mark King (QF 2)
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