Williams hit three centuries, including a 140 break, as he raced to an incredible 9-0 lead in a best-of-19 match, leaving him one frame away from completely whitewashing his Northern Irish opponent.

However, Allen held his nerve to win the 10th frame, declaring to laughter from the crowd: "No one beats me 10-0."

Allen then went on to win the following four frames as he looked to launch an improbable comeback, but Welshman Williams stopped the resurgence in the 15th frame to cement his place in Sunday's final.

"I did a great break there really," Williams told ITV of his winning frame.

"As good as any I did in the whole match. I just knew I had to make a one-frame visit the way the match was going.

"I try to get my practice at the venues. I've been playing like that all season. Some of the people have played unbelievable snooker against me this season.

"If I had a pick to play in the final, it would be O'Sullivan. He's the best player by a mile at a packed venue."

O'Sullivan had earlier beaten Gary Wilson 10-7 in what was a tense semi-final in which Wilson pushed O'Sullivan all the way.