O'Sullivan, the defending champion, lost all his concentration and looked bored as the penultimate frame became scrappy.

When he played a shot he found particularly poor he motioned with his cue between his legs and Tabb stepped in to issue a brief reprimand, with O'Sullivan seeming to say "I wanna go home", albeit jokingly.

It was not a formal warning from Tabb and O'Sullivan denied trying to cause offence, apparently arguing his cue was sticky and he was trying to solve the problem.

He lost the frame but took the last of the night with an 89 break to move 14-10 in front, three away from his fifth World Championship final.

Having begun the day level at 4-4 in the match, to come through two sessions with a four-frame cushion was a fine achievement for O'Sullivan.

Trump had the session's highest break of 117, the first century of the match, but he required a remarkable comeback this afternoon.

Four-time champion O'Sullivan has suggested the sport's ringmaster Barry Hearn has the pulling power to ensure he is not lost to snooker forever.

World Snooker chairman Hearn, who has managed O'Sullivan in the past, has vowed not to stand in the 37-year-old's way should the latest in a long line of retirement warnings be one he sticks to.

O'Sullivan said: "You never know with Barry, he's always changing things.

"He might go, 'Look Ronnsy, I've got a little tournament for you, you can turn up, do two weeks' practice'.

"And I might go, 'You know what, I'm up for that'."

Last-four debutants Barry Hawkins and Ricky Walden were resuming play in the second semi-final this morning, before the match reaches what could be a tense climax tonight, with neither man used to such occasions.

Chester's Walden led 9-7 overnight, but after firing three centuries to a best break of 47 from Kent cueman Hawkins he would feel he should be further ahead.