The `Rocket’, who roared back from 3-0 down to defeat Joe Swail 5-4 in the previous round, despatched Alan McManus 5-1 in just 77 minutes and now meets another Scot — Graeme Dott — for a place in Sunday’s final.
He compiled another two century breaks — 131 and 103 — to take his tally to five in two matches and establish a virtually unassailable 4-0 interval lead.
McManus at least managed to avoid a whitewash by stealing the fifth frame with a 31 clearance but O’Sullivan wrapped things up with a run of 42 after his opponent had sportingly called himself for a foul after brushing the green with his fingers.
O’Sullivan won six titles last season and the 25-year-old from Essex is keen to get the first one under his belt this season. However, he is not taking anything from granted.
Dott, his semifinal opponent, led O’Sullivan 4-0 in the semi-finals of last year’s Regal Scottish only to lose 6-5. The world No 12 will be out for revenge tomorrow.
Dott ended the giant-killing run of Ali Carter to reach the semi-finals. World No 61 Carter went into the match as 5-6 joint favourite with the sponsors on the strength of his previous victories over James Wattana, Paul Hunter and world No 1 Mark Williams in the pounds 666,800 event.
But it was Dott, who has broken into the game’s elite top 16 for the first time this season at No 14, who emerged the 5-3 winner.
The 24-year-old from Larkhall in Glasgow, like Mark King before him, is now through to the third ranking semi-final of his seven-year professional career, having finished runner-up to Stephen Hendry in the 1999 Regal Scottish.
Breaks of 83 and 50 helped Dott establish a 3-1 interval lead and although Essex boy Carter closed to 4-3 behind, he was unable to overcome a 56-15 deficit in the eighth frame, even though his opponent showed signs of nerves by missing what amounted to a match-ball black.
Defending champion Peter Ebdon was whitewashed by Mark King.
Ebdon, who went into the match the 1-2 favourite, was outplayed from start to finish by the world No 13 and scored only 59 points in five frames.
King, through to the semi-finals of a world ranking tournament for the third time in his 10-year professional career, could hardly believe it as he was presented with chance after chance by the normally miserly Ebdon.
It was not as though King scored heavily — his highest break was 46 — but he past 30 on six occasions and that proved more than enough on the day.
Ebdon admitted to being shell-shocked by the result. “I honestly came here expecting to win the tournament again this week,” said the world No 7. “It was a strange match. Every time I missed I seemed to stick him up.”
John Higgins produced an ice-cool clearance to keep his hat-trick hopes alive.
Higgins, winner of the first two tournaments of the season — the Champions Cup and Regal Masters, looked as though he would be spending the weekend with wife Denise and new son Pierce when he trailed Stephen Lee 53-4 in the ninth and deciding frame.
But Lee missed the pink to the right-hand centre pocket to throw the world No 3 a lifeline and he took it with a superb clearance of 52 to win on the black — his ninth victory in 11 meetings with Lee. He now plays Mark King in tomorrow’s first semi-final.
Nobody could say the 26-year-old Scot did not deserve it. He looked like winning the match 5-3 until he went in-off the final red escaping from a snooker. Then he potted the green in the decider and went into the pack only to see a red drop into the top left-hand pocket.
Mark King (Eng) bt Peter Ebdon (Eng) 5-0; Graeme Dott (Scot) bt Ali Carter (Eng) 5-3; Ronnie O’Sullivan (Eng) bt Alan McManus (Scot) 5-1; John Higgins (Scot) bt Stephen Lee (Eng) 5-4.