Nick Watney climbed into a tie for second place at 11-under-par 205 thanks to a third-round 66. He is joined there by David McKenzie (70), who shared the lead entering the third round with Hearn. Mathew Goggin stands alone in fourth place at 9-under-par 207, while Kevin Johnson is one stroke further back at minus-8.
Hearn was steady over his opening nine holes. He parred the first four holes, before collecting a birdie at the fifth. He then ran off four straight pars to make the turn at minus-10.
The 25-year-old Canadian then dropped in back-to-back birdies from the 10th at Redwood Meadows, the second of which came after an 80-minute rain delay. Hearn picked up his third birdie of the back side at the par-3 13th to get to 13 under.
Hearn coasted to the last with four consecutive pars. At the 18th, Hearn dropped in a 30-foot birdie putt to move three strokes clear of the field and close out a bogey-free round.
'It all boils down to going out and trying to hit targets,' said Hearn, the fourth leading money winner on the Canadian Tour this season. 'I was hitting it pretty well, but I didn't sink a lot of putts. I was trying to stay as patient as I could. I'd say my focus was about as good as it could get today.'
Watney roared up the leaderboard as he caught fire midway through his round. The 23-year-old bogeyed the first, but turned it on at the sixth. Watney ran off three birdies over a four-hole stretch from the sixth to jump to 7 under.
After a par at the 10th, Watney birdied the 11th and 12th before dropping another stroke at the 13th. The Fresno State alum converted back-to-back birdies from the 14th to move to minus-10. He closed with a birdie at the par-3 17th.
'I had a good day,' Watney said. 'I putted real well and kept the ball in play and it all added up to 6 under. I struggled yesterday and I needed to get back in the tournament, so I think today's 66 was better than the one I shot in the opening round.'
McKenzie got off to a hot start with birdies at the first and third. He cooled off, however, as he played even-par golf over his next six holes. He wrapped bogeys at the 10th and 12th around a birdie at the 11th. The Australian rolled in a birdie at the 15th before parring his final three holes to share second place.
Charles Warren carded a 2-under 70 in the third round to move into a tie for sixth place at 7-under-par 209. He is joined there by Jason Schultz, Paul Gow, Matthew Jones, John Morse and Jason Buha. Wes Martin and Erik Compton are one stroke further back at minus-6.