Williamson and fellow American Stephen Gangluff stand at 11-under-par 205 for a two-shot lead heading into the final round Sunday.
Gangluff shot a 4-under 68 in his third round, but the real move was made by Williamson, who entered Saturday in 22nd place.
Williamson began making strides with a birdie at the par-5 fifth -- the first of seven birdies he collected in an eight-hole stretch to move to 10 under.
He made two putts longer than 20 feet during the run, and also stroked a seven iron within one foot at the par-4 sixth.
Williamson added another birdie at the 15th, his third straight birdie at the par-5 hole.
'It sure was a good day for me,' said Williamson, who won his first Canadian Tour title last year at the MTS Classic. 'I just played really well all around.'
Gangluff was cruising through 12 holes -- collecting six birdies during that stretch -- but went on to bogey three of his final six holes. He held a two- shot lead before three-putt bogies on 16 and 18 dropped him back to minus-11.
'I would love to be able to say I played perfect and did everything right, but if you played perfect every day it wouldn't be much of a contest,' said Gangluff, whose round also included a hole-out for birdie from a bunker on No. 10.
'That's the way this game is. You have to take the good with the bad.'
Ron Harvey, Jr. shot a 2-under 70 in his third round to move into third place alone at 9-under-par 207. Travis Johnson and Justin Lee are one stroke further back in fourth place after matching 69s.
Overnight leader Dong Yi imploded on Saturday, sputtering to a 7-over 79 to fall into a tie for 34th place at minus-1. Yi's round included a triple-bogey at the first hole as well as two double-bogeys and two bogeys.