Neil Robertson played the shot of his life to set up a match-winning century as the defending Betfair Masters champion edged out Mark Allen 6-5 to reach the semi-finals.

With a thrilling contest into a deciding frame, Allen put Robertson in all sorts of trouble when he ran through off a red to tuck in snug behind the yellow which was just off its spot.

Robertson's only real chance of an escape was to target a red hanging over a top pocket, and Allen could do nothing but watch as his opponent went off the baulk cushion and down to the pocket, clipping in the red and landing on the black.

From there the Australian made a classy 105 to win the match, before being congratulated by Allen.

But while a dejected Allen labelled Robertson's shot a "fluke", the 30-year-old Australian insisted it was played with the highest degree of skill.

"It was like trying to read a really horrible putt on a green. In terms of judgement it was probably the best shot I've ever played," Robertson said.

"It's lucky but it's not a fluke.

"The blue was in the middle of the table and that makes it quite tough, so I had to play the white in a certain way that the white will arc and miss the blue and then to judge the pace and pot it and still be on the black."

Speaking in the immediate aftermath of the Alexandra Palace tussle, Robertson said of his remarkable shot on BBC2: "You'd get it maybe one in 10 times. I had to apologise to Mark. It's a hard way to go out of the tournament from his point of view."

Robertson made three centuries in the match but Allen was a hard man to shake off and a break of 138 in the fourth frame inched ahead of his own 136 to become the highest break in the tournament so far.

Defeat, therefore, was painful for the 26-year-old, who believes he is playing well enough to go further on the big stage.

"It's a hard one to take in the final frame," Allen said. "You're only looking for one chance and I thought the safety was going to give me that chance.

"Hopefully on another day that might happen to me but it just doesn't seem to be going my way at the moment.

"My safety wasn't the best and I think that's what cost me. My safety wasn't anywhere near as good as Neil's, and against in my opinion the best player in the world it has to be a lot better."

Allen was pleased that Robertson played it cool at the end of the match, rather than roaring his delight.

"I was sitting in my seat, thinking that if he says 'You beauty!' after this I was going to crack up. But he didn't, he's a good sport," Allen added.

"He only fluked one ball, he still had to go and pot the rest. Not many players would have made a century from the way the balls were sitting."

Robertson has tomorrow off before a semi-final showdown on Saturday afternoon against the winner of tonight's second quarter-final between John Higgins and Shaun Murphy.