Ricky Walden stretched his lead over Barry Hawkins in their Betfair World Championship semi-final this morning.

From 9-7 ahead at the start of play, Walden pulled 12-8 clear, meaning he required five more frames to reach his first Crucible final.

After taking a scrappy opener, Walden delivered a crushing blow to Hawkins' hopes in the second frame of the session.

A break of 62 from Hawkins was his first of 50 or above in the match, and came to an end when the white appeared to take a heavy bounce off the side cushion and cosied up to the black, forcing him to play safe.

Walden cleared up with 63 to take the frame on the black, opening a four-frame lead.

After his struggles in the opening two sessions of the four-session contest, Hawkins was at least scoring more heavily today, and 114 from the Kent cueman made it 11-8.

However it was the only frame he claimed before the mid-session interval, as Walden went to the break with a run of 78, capitalising after Hawkins potted the white.

Fresh controversy surrounded Ronnie O'Sullivan as his semi-final against Judd Trump moved towards its conclusion. They were due to play to a finish in the afternoon session.

O'Sullivan, who was fined £20,000 in 1996 for head-butting a tournament official behind the scenes at the Crucible, and who on Wednesday announced this would be his Crucible swan song after returning to the game only to make some quick money, was ticked off by referee Michaela Tabb for what the Scot perceived as a rude gesture during last night's third session of the match.

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, saying: "Ronnie, don't make obscene gestures again okay, or I'll need to warn you."

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.

Discussing O'Sullivan's behaviour, seven-time world champion Stephen Hendry said on the BBC today: "He's always been very impulsive and he just does things if he's not happy with his game."

There was also a bizarre episode yesterday during O'Sullivan's match that saw tournament security officials have to remove a remote-controlled device planted inside the auditorium that was making flatulence noises.