World champion Ken Doherty survived a war of attrition with Scotland's Jamie Burnett in Bingen last night to become the first player to reach the semi-finals of the £280,000 German Open.

Doherty, runner-up to John Higgins at the inaugural event in Frankfurt two years ago, was never ahead until he clinched the final frame for an unconvincing 54 victory.

But he could easily have been heading home to Dublin as Burnett missed a final green in the decider when on target to clear up and win by a single point.

Doherty did not miss the same ball, which left the world number 38 from Hamilton requiring a snooker, and Burnett eventually conceded on the blue to bring to an end a four-hour, five-minute marathon.

It was hard luck on Burnett, who had led 3-1 and, with better fortune, might easily have been 40 up.

The third frame, settled on the final black, proved the major turning point.

Doherty levelled at 3-3, including a break of 103, and though Burnett went ahead again at 4-3, Doherty responded to win a 40minute eighth frame with a break of 40.

"We Paddies never know when to give up," said the 28-year-old world number three. "I came back from the dead, because there were several times when I thought I was out. My only consolation is that I can play better. As far as this is concerned, a win is a win.

"When Jamie got in during that last frame I could see him clearing up, but you need a little bit of luck and I got mine in this game."

Burnett was not too disappointed after pushing Doherty so close, and said: "He showed he is a true world champion by the way he came back. I missed the green not because I felt the pressure but because it was a difficult shot.

"I had to play it slowly with a lot of check side after playing a poor positional shot on the yellow." Later last night, Ronnie O'Sullivan fluked the final black of a deciding ninth frame to deny unlucky Tony Drago a place in the semi-finals.

"I went for the double but not the treble," grinned the defending champion after completing his exciting, 5-4 victory. "But I know I can't keep relying on luck if I want to retain my title."

London-based Drago had been in command throughout the decider having trailed 3-1 and 4-3. He led 39-1 when he made his first error.

He failed to pot the blue but that was not as crucial as his error on the pink when poised to reach the semi-finals of a ranking tournament for only the second time in his 12-year career.

Drago took aim into a top pocket and missed and then several minutes later jawed the black into the yellow bag that would have given him victory.

"I honestly thought the black was in," said the world number 11. "But both of us were a bundle of nerves in the last frame.

"To be honest, I believe justice was done in the end even though Ronnie fluked the black.

"In the sixth frame he was sporting enough to let me take a shot after the balls had gone everywhere the previous shot.

"There was no way we knew where the balls were meant to be and neither did the referee. I managed to make a break of 73 when probably I could easily have lost the frame."

German Open (in Bingen) - Quarter- final: K Doherty (Ire) bt J Burnett (Scot) 5-4. (Frame scores, Doherty first: 1-101, 19-90, 6052, 37-67, 128 (103)-0, 72-20, 22-66, 66-26, 6832.) R O'Sullivan (Eng) bt T Drago (Mal) 5-4. (Frame scores, O'Sullivan first: 102-36 62-74 8522 67-20 24-84 7-113 90-0 56-71 63-51.)