World number 17 Williams dominated the final against Thailand’s Un-Nooh to take the top prize of 3.5 million Baht (around £81,000).
It’s a first title for Welshman Williams since he won the World Seniors Championship in 2015.
Un-Nooh, who won this invitational title in front of his home crowd two years ago, started well with a break of 71 to take the opening frame, and was tied 2-2 after four frames. But two-time World Champion Williams then took control and won the last six frames with a top break of 50, restricting his opponent to just 30 points in that spell.
“When I came here I didn’t have any great hopes of winning this,” said 42-year-old Williams, who is using a new coaching methodthis season in a bid to regain his best. “I battled away and I’m so pleased to win an event. Today was the best I played all week. I wasn’t looking to make any big breaks, just to win frames.
“I think over the years I haven’t got any further than the last 16 of this event so I suppose I’ve surprised myself this week. I’ve won a lot of money playing in Thailand and China and I’ve become a good traveller.”
World number 39 Un-Nooh, who earned 1.3 million Baht, said: “Mark played very well. I couldn’t take any chances and when I missed he had all the answers.”
Polapatr Suvarnazorn, advisor to the president and CEO of the Thai Beverage Public Co.Ltd, presented the winner’s cheque while WPBSA chairman.Jason Ferguson handed over the runner-up prize.
Frames (Williams first) 0-71(71); 49-0;55-1;32-37; 39-0; 38-9; 54-0; 50(50)-0, 49-6;43-15.