Grob, the Canadian Tour's all-time leading money winner, carded a 5-under 65, while Jon Turcott equaled the course record on Saturday. He fired a 7-under 63 and is tied for third place with Dustin Risdon, who shot a 3-under 67. The pair is knotted at minus-7.
Guetz did not get off to a great start in round three. He bogeyed the second and fourth holes, but birdies at six and nine allowed him to make the turn at even-par 35.
Many players took their turn atop the leaderboard including Risdon, but a double-bogey at the 12th dropped him down. Guetz was back in front, but a bogey of his own at 14 gave Risdon back the lead.
Risdon bogeyed the last to drop to minus-seven. Guetz rolled in a 30-foot birdie putt at the closing hole to move two clear of Risdon. Grob birdied two of his last five, but is still looking up at Guetz.
'It's tough, just when you think you are going to get it going, you hit a wall,' said Guetz. 'But I'm right where I want to be. Anything can happen tomorrow. It should be a lot of fun.'
Guetz will be in search of his first win on the Canadian Tour.
Jason Hartwick (70), Todd Tanner (68), Wil Collins (67) and Wes Heffernan (67) are knotted in fifth place at 6-under-par 204.
John Lieber, who shared the overnight lead with Guetz, struggled on Saturday. He posted a 2-over-par 72 and is tied for ninth place with Brad Fritsch, who shot a 66, at minus-5.