Neil Robertson stayed on course for his third title in four months by beating Mark Allen 6-4 in the Welsh Open semi-finals - as a foul in the third frame turned the match on its head.

The 34-year-old Australian won the Champion of Champions in November and the UK Championship in December, and is now just one win away from what would be his second Welsh Open crown and 12th ranking title of his career.

The match turned on an incident in the third frame when Allen accidentally fouled when set to go 3-0 up, and Robertson took advantage to win six of the last eight frames.

Allen won the opening frame with a break of 77 and started the second with a run of 55 before punishing Robertson for missing a tricky brown off the last red.

But in frame three Allen was on 56 when he potted a red with the rest, and referee Terry Camilleri called a foul as he felt the Northern Irishman had grazed another red with his cue.

A video replay proved that the referee was right and Robertson later capitalised with a superb 49 clearance before breaks of 54 and 51 in the next frame made it 2-2 at the interval.

Robertson, the world number three, kept his momentum going after the interval with breaks of 75, 82 and 72 to go 5-2 up.

Allen hit back with a 124 and took the next as well to close to 5-4 before having the chance to force a deciding frame.

But he rattled a tough last red in the jaws of the top pocket, and Robertson eased home to keep alive his hopes of repeating his 2007 Welsh Open triumph.

Ronnie O'Sullivan or Joe Perry will meet Robertson on Sunday, with the pair contesting their semi-final on Saturday night.