The current UK champion's win was his ninth in succession in ranking events as he demolished the Englishman in the evening session by claiming the final five frames.

Williams could have won even more comfortably. He lost two black ball frames in the first session and finished all square at 4-4 after O'Sullivan scored 208 points without reply at the end of the afternoon.

Williams was fortunate to fluke a green at the start of the second session that enabled him to make 47 and regain his lead.

Reflective Ronnie

Without ever looking totally in control Williams scrapped his way to the next three frames to lead 8-4 at the final interval.

O'Sullivan's progression to the last four had been a battle because of motivational problems, but he was comprehensively beaten by Williams who claimed breaks of 66 and 63 in the match.

Williams will now meet either Stephen Hendry or John Higgins in Sunday's best-of-19 frames final for the championship crown but the Welshman was still not convinced by his performance.

"To me it doesn't matter how I win as long as I do. Knowing how I can play, that was rubbish," claimed Williams.

"I can miss easy shots one minute and pot a lot of good ones the next. That's how it's been throughout my career.

O'Sullivan will now head to the Far East to defend his China Open title and he was in reflective mood after his defeat.

"I've just lost a snooker match and I'll probably lose many more," shrugged O'Sullivan.

"It's just part and parcel of being a sportsman. I've made hard work of winning my matches this week but I was beaten by a better player."

Frames scores (Williams first): 78-38 57-58 56-59 66-1 66-0 45-35 0-116 (116 break) 0-92 68-0 79-9 92-16 90-38 58-53