Ken Doherty has been talking about another gear all week. Yesterday he found it.

In the first session of his semi-final match against Welsh number four seed Mark Williams, Doherty combined his experience and tactical acumen to dominate a sometimes impetuous but dangerous opponent.

After two-and-a-half hours, the reigning World Champion worked his way from an initial 3-0 advantage to take a 6-2 lead at the close with some of the most satisfying snooker he has played all week.

"I would have been happy to come out of the first session 5-3 ahead but 6-2 is even nicer," he said. "Winning that last frame when I needed two snookers was a real bonus. I thought Mark was going to clear up until he missed the yellow. He also missed the yellow in the previous frame when he got a kick."

If body language could talk, William's would probably tell a depressing story. The funereal disposition and hangdog manner of the 23-year-old rarely changed throughout the session, during which Doherty's opportunism and ability to build from modest breaks took him through quite comfortably.

In truth, the Irishman was occasionally fortuitous as Williams demonstrated flashes of rash judgement and hasty play as well as an ability to pot. For this session, however, he will be remembered more for his misses than for his potting.

In the final frame of the session, Williams was offered a free ball after Doherty had failed from a snooker. Williams chose a simple yellow pot into the green pocket only to point at the white ball in astonishment as the yellow ricocheted around the jaws and then refused to go in, letting Doherty in for a 71-54 frame.

Doherty also claimed another very tight frame in the fifth when he clawed his way back through the colours to tie the game 47-47. He subsequently potted the respotted black to claim the frame for a 4-1 advantage.

"It was a bit of a scrappy session although I think it was fairly exciting for the crowd, especially the fifth frame and the re-spotted black," said Doherty.

From the beginning, the Irishman has said his focus will remain on one session at a time. In this 33-frame match, the first is but a few steps on what will be a long journey, with two more sessions programmed for today and the final nine on Saturday afternoon.

"There is still an awful long way to go in this match and Mark is, a dangerous opponent. But naturally I am delighted with the start I've made so far," added Doherty.

The scrappy play the champion spoke of was illustrated by the fact that his highest break was 45 in frame one. Breaks of 42 and 38 followed but nothing to break 50. Doherty, however, looked relaxed and purposeful throughout and even provided a moment of light relief to the packed house much to the mortification of a latecomer to the match.

As the Irishman was about to stroke the white in the second frame, a noise startled him and he stopped. He again addressed the ball but was again distracted and moved from the table.

Standing back and looking into the crowd he waited as the gent rustled around in the wrong row of seats oblivious that he was being watched by the entire auditorium and by the television cameras.

"In your own time," shouted the player, causing the crowd to chuckle and the patron to flee. Doherty proceeded to win the frame.

Williams has never advanced beyond round two of this competition, going out 13-8 to Stephen Hendry last year. Before that he never advanced beyond the qualification rounds.

But he has had a meteoric rise up the world ranking list, climbing from 119th to fourth in just four seasons and establishing himself as one of the sharpest talents in the game. He has also accounted for Steve Davis and a fancied Peter Ebdon in the previous two rounds.

John Higgins missed out on a £166,00 jackpot as the chance of a maximum break went begging in his semi-final with Ronnie O'Sullivn. Higgins has never even managed the magic 147 in practice, but he looked like ending that record when he potted 13reds and blacks in the fourth frame of a thrilling opening session, which ended all square at 4-4.