Daniel DeLeon carded a 3-under 68 and is alone in second place at minus- 8. Canadian Tour money leader Jamie Gomez also shot a 68 and has sole possession of third at 3-under-par 210.
Williamson flew out of the gate on Saturday with four birdies in his first six holes. At the insanely difficult par-3 ninth, Williamson landed in a greenside bunker, but saved par from 3 feet.
He made the turn with a two-shot lead over DeLeon, but DeLeon birdied three in a row from the 12th to take first. Williamson drew even with a 30-foot birdie putt at the 15th and DeLeon dropped out of the top spot with a bogey at the last.
Williamson missed three birdie putts inside 7 feet, but the 26-year-old runner-up at the U.S. Public Links Championship in 2002, is content with his position.
'I am very happy,' said Williamson. 'On the front, I got the most I could out of it. It had that frustrating run with the missed putts, but I was determined to cash one in. It was a great way to get back on track.'
Williamson will be in search of his first win on the Canadian Tour.
DeLeon knows Williamson will be the man to catch, but it's not a two-horse race.
'It may seem like it's the two of us, but there are a lot of guys that can take it low here,' said DeLeon. 'This wind was tough, it really makes you think twice about your shots. I made some mental mistakes over-concentrating. I'll take my same approach as I've had all week on Sunday. It's all about patience, and hopefully that will be enough.'
Marcus Jones shot a 3-under 68 and is alone in fourth at minus-2.
Mike Grob, who can become the Canadian Tour's all-time money leader with a top-four finish, struggled to a 4-over 75 and is tied for fifth place with Brien Davis (71), Ryan Ellis (67), Luke Hickmott (66) and Dustin Risdon (69). The group is knotted at 1-under-par 212.