Petrovic fired a 6-under-par 66 at the DiamondBack Golf Club to earn a share of the lead entering the final round in Toronto, Ontario.
At 11-under, Petrovic is tied with Kevin Burton (69) and Richard Zokol (70). Gary Hallberg (68), Richard Johnson (67) and Pat Perez (67) are one shot back.
Petrovic, a 34-year-old former Pizza Hut deliveryman, is in search of his first Buy.Com Tour victory.
He started the day four shots back of Zokol, but birdied four of his final five holes Saturday to make up the ground.
Zokol is one of only four Canadians to make the cut. He led through 36 holes, but dropped out of the top spot with a double bogey at the par-3 15th. However, Zokol rebounded with a birdie at the par-5 18th to regain share of first place.
Full-field scores from the Canadian PGA Championship