The 35-year-old had only recently returned to the sport after being banned.
In April 2010 Higgins and his manager, Pat Mooney were filmed in a sting operation conducted by the News of the World newspaper.
Higgins was cleared of match fixing on 8 September 2010 following a tribunal. However, he was found guilty of bringing the game into disrepute by not reporting the approach the News of The World made towards him.
John Higgins received a six month ban and fined £75,000
"I was a man on a mission. I was really determined to try and stop anything which prevented me from winning it," Higgins said.
"Given everything that surrounds it, this is my finest hour on the table. It means everything, just to be back playing and winning. It means a great deal.
"Obviously it means a great deal to my family as well."
He added: "I just never gave up. I thought 9-5 was too big a mountain but each frame was going past and I was still in it. It is an unbelievable feeling."
Higgins down and out after slipping down 7-2 and then 9-5 but Williams was unable to finish off the match after moving to the brink of victory.
"John done well to come back to be fair to him," the defeated Welshman said.
"I felt the gods were against me on a couple of occasions but I have got no complaints overall.
"I have been pretty dreadful all week. That was probably the best match I played all week. The best player in the tournament won but I had a chance to nick it and probably threw it away."
