O'Sullivan shrugged off the handicap of mid-match tip problems to secure a 5-4 victory over John Parrott after trailing 4-2. He now plays Peter Ebdon, who recorded his second victory over Ken Doherty in less than a week, this afternoon.
Despite the win O'Sullivan was unhappy with his patchy performance. "I badly want to win everything I enter but today I was there for the taking," he said.
"I wasn't sighting the balls properly, I didn't know where they were going and I wasn't in control. Luckily I started to click before it was too late."
A superb 141 total clearance, bettered only by Stephen Hendry's run of 145 two years ago as the tournament's record break, saw O'Sullivan power 2-0 ahead before his cue tip began to detach itself.
By the time emergency repairs were carried out by the ITV commentators John Meadowcroft and Mike Howett at the mid-session interval, the score was 2-2.
When Parrott added the following two frames as well, the title holder looked on course for a premature exit but O'Sullivan somehow engaged a higher gear.
Earlier, Alan McManus edged out fellow Scot John Higgins 5-4 to clinch a place in the semi-finals.
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