O’Sullivan, the world number one and defending champion, looked in total control as he breezed into a 3-0 lead with breaks of 115 and 79, but Williams fought back to lead 5-4 before taking the deciding frame with a break of 102.

Williams, a two-time Masters champion who last won the competition in 2003, told the BBC: "In the first three frames I didn't have a shot, he tied me up in knots but I felt the crowd wanted me to win towards the end, that is unbelievable.

"You are playing the greatest player ever, if I don't beat him for another 20 years I don't care. It is up there as my best performance. I fancied beating him."

Asked whether he would go on to win his third title, the 47-year-old said: "I am not going to go that far. I have been playing well for a while and I am over the moon."

A disappointed O'Sullivan said: "I just didn't score, didn't make any breaks and my cue ball wasn't great. I hung in there, the battling qualities forced a decider.

"He played the better snooker and was more clinical. I was happy to get it to five and, when you are not playing well, those blacks can be missed."