Williams, no stranger to tight finishes, having sunk a re- spotted black to edge out Stephen Hendry in this year's Benson & Hedges Masters final, held his nerve to put the seal on a 6-5 Welsh victory over Northern Ireland.
"What happened in Bangkok was on my mind, and I was shaking all over," said Williams, referring to his defeat to Thailand's James Wattana in an equally tense climax to the World Cup quarter-final.
Northern Ireland led 2-0 but trailed 3-2 when they put together a three- frame spurt which threatened to scupper any hopes of Wales appearing in Sunday's final.
Jason Prince had a 40 break in overcoming Williams before veteran Dennis Taylor brought his vast experience to bear. The 1985 world champion, who celebrated his 50th birthday on Tuesday, ground out a 39-minute singles triumph over Matthew Stevens before a 52 break helped he and partner Terry Murphy win a vital doubles contest.
That pushed Northern Ireland into a 5-3 lead and onto the verge of chalking up their second success of the week, having beaten England 6-5 on Monday. But Williams then sneaked past Murphy with a last red to blue clearance which launched the Welsh revival.
It continued when Stevens shaded Prince on the blue in frame 10 and was completed when Williams retained sufficient composure to clear yellow to blue in the decider, after potting a crucial green from distance. The Welsh quartet must now beat England tomorrow to guarantee an appearance in the final.Reuse content