The 32-year-old Londoner stunned two-time UK champion Ding Junhui with a 6-4 win yesterday, at the same time another former York champion Judd Trump, exited the tournament after a 6-4 loss to Joe Perry.
Trailing 3-2 to Sheffield-based Ding, O’Donnell secured victory with breaks of 44, 49, 90 and 41.
But facing O’Sullivan will be a different challenge today for world No 59 O’Donnell, who has come up against Chinese players in every round on his way to the last eight at the Barbican, where he is set for the biggest pay day of his career.
“I’m not here just to get to quarter-finals so I haven’t achieved anything yet,” said O’Donnell, who before this season had never gone beyond the last 16 in a ranking tournament.
“Ronnie is the greatest player ever and it will be a privilege to play him. I’ll just keep doing what I’m doing and take the game to him. I practise six or seven hours a day believing that when I get my chance I’ll be able to take it.
“A lot of players seem to struggle to play their own game against Ronnie. I’ll find out tomorrow what it’s like to play him.
“He’s got that aura around him. But I’ll just focus on my own game and see what chances I get. That will be the challenge for me, not to look over at him in his seat or worry about what he’s doing. I’ve got to stay calm, be patient, be aggressive and see what happens. He could beat me 6-0 and it has still been a good tournament for me.
“I have sat in many venues watching Ronnie and cheering him on myself. I’d imagine the crowd will be one-sided tomorrow. But crowds like a battle so hopefully I can stand up and produce that.”
Fifth seed Trump – the 2011 UK champion – was 3-1 ahead before trading centuries with Perry, who then pulled away before clinching a deserved victory with a 136 clearance, and secure a quarter-final against Tom Ford.
Kyren Wilson reached the quarter-finals with a 6-2 win over Barry Hawkins, and he will play former world champion Stuart Bingham after a 6-2 victory over Thailand’s Sunny Akani.