THE dictionary defines the crucible as a vessel in which metal is heated until it liquefies. As May Day and political temperatures soared in Britain yesterday, some of Ken Doherty's friends and supporters came dangerously close to meltdown at the Crucible Theatre in Sheffield as he battled to retain parity in his world snooker championship semifinal with Alain Robidoux from Canada.

It was a tense affair from the start, and Doherty admitted later that the pressure of being in such an important contest in what is regarded as the Cathedral of world snooker had affected his concentration. "I was nervous, yes. With only one table in play today I was very aware that our match was the centre of all attraction, and I think that got to me.

"But I am happy that I am on level terms after some poor potting. With 25 frames left I that I can play better in the next three sessions and go on to play in the final. That is my aim at the moment.

"I know that people at home are watching and praying. I know I am good enough and that I can shake off today's nerves and do myself justice in the rest of the match," he said.

It is fair to say that the tension seemed to affect Doherty more than Robidoux as the Dubliner failed on several important junctures to pot reds which he would normally sink with his eyes closed, so to speak. His opponent was never in any mood to allow any respite; he turned the screw at every opportunity.

There were times, too, that Doherty was at odds with the snooker gods. Twice in the match he saw the cue ball go down after potting a red, and an extraordinary fluke in the third frame amazed all of the onlookers: Robidoux went for an easy looking yellow in the left baulk pocket, only to see it bobble off both pocket jaws, drift down to the cushion at the other end and rebound to kiss the pink on its way into the middle pocket on the right.

No wonder Robidoux bowed his head and blushed above his goatee. We all realised then that his trick shot title of "The Montreal Magician" was well earned and deserved.

In fairness, Doherty got his own back later when, first, the cue ball hovered tantalisingly over the pocket after a safety shot, and then more outrageously when an attempted red in the final frame of the session saw it rebound from the jaws of the pocket and sneak across the table to find refuge in the other corner.

In the opening frame, Doherty took the initiative, after a nervous start, with a break of 66 which included six blacks and left Robidoux needing snookers. Doherty took the frame 104-5.

Breaks of 24 and 58 gave the second frame to Robidoux, and the Canadian took the third 78-33 with three small breaks.

Doherty seemed to have put his nerves behind him when he totted up scores of 35 and 60 to take the next, but impressive breaks of 69 and 62 put Robidoux 3-2 ahead.

The sixth frame was one of mixed fortunes as Doherty started with a break of 24, and after a couple of hiccups added another break of 32, to win the frame 62-26.

Once again Robidoux slipped into the lead after an opening break of 32 and a bad miss on the red by Doherty allowed the Canadian back onto the table for a break of 25, which eventually gave him the frame 67-23.

The final frame of the session seemed to indicate that Doherty was finally taking control, and a 75, the biggest break of the session, gave him a well deserved share of the afternoon's spoils.

James Wattana overcame a mid session crisis to grab a semi final lifeline against Stephen Hendry. The 27 year old from Thailand took the final frame in the opening session to trail 5-3 after losing five in a row.