Grob, the Canadian Tour's all-time money leader, finished four rounds at 11-under-par 269 for his fourth tour victory and first since the 2002 Ontario Open Heritage Classic.
'I'm getting up there. I'm a little older than the rest of these guys. There are a lot of young guns out here, so it means a lot to know I can still get it done,' said Grob, a 42-year-old father of two.
Six-time Canadian Tour winner Trevor Dodds matched the professional course record with a 7-under 63 at Royal Colwood, but it wasn't enough. He finished tied for second place with John Lieber (65) at 10-under-par 270.
Wes Heffernan (68) and Jon Turcott (69) shared fourth place, two shots further back.
Grob trailed third-round leader Bret Guetz by one shot overnight, but while Guetz was busy going 4-over on his first three holes, Grob opened with five straight pars to take the lead.
A birdie at the par-3 sixth moved Grob further under par. Around the turn, he was tied with Turcott for the lead -- but Turcott bogeyed No. 10, and Grob picked up another shot with a birdie.
After a birdie at the par-5 14th, Grob rolled in a 30-foot putt at the par-4 17th for another birdie and a two-shot lead.
The extra stroke came in handy after he blasted his tee shot right at the 18th and two-putted for bogey.
'I kept saying to myself 'Left is okay, left is okay,' and what do I do but bail to the right,' Grob joked of his tee shot. 'I thought I sealed the deal with that putt on 17. I knew 18 would be tough and it gave me a little breathing room.'
Wil Collins, Brad Fritsch and Dustin Risdon shared sixth place at 6 under par, one shot better than Steve Friesen, Christopher Botsford and John Mallinger.
Guetz, the overnight leader, stumbled to a 5-over 75 and finished at minus-4.