The 1997 world champion failed to "nd any form as he fell at the quarter-"nal stage. O'Brien, the 1999 British Open champion, will face seven-time world champion Stephen Hendry or Barry Hawkins in the semi-"nals.

"I don't think I've ever whitewashed Ken, he's such a good match player, " said O'Brien. "I can't ask for a better result than that. I had a dream start and didn't put a foot wrong to lead 4-0."

The turning point in the match came when O'Brien pinched the third frame when well behind. Trailing 58-0, O'Brien pocketed a 59 clearance and never looked back.

"I won a deadly third frame, " he added. "I felt a bit of pressure in the last frame because you know with Ken he never gives up, so to get over the winning line is important. We both knew before that there was going to be one Irishman in the semis, I'm just glad it's me."

O'Brien was dominant from start to "nish and of 96, 49, 59, 69 and 47 did the damage as O'Brien triumphed in just under two hours.