Reavie, who will go for his first tour win on Sunday, completed 54 holes at 13-under-par 203.
Kyle McCarthy, who led after the first two rounds, posted his second straight 70. He is alone in second at 12-under-par 204. Jon Mills is alone in third at minus-11 after a 68 Saturday. Tommy Biershenk matched Reavie's 65 to jump into fourth place at 10-under-par 206.
Reavie, who began the day tied for seventh, got going with a birdie on the second. He came back with birdies on five and seven to move to 9-under.
The 25-year-old birdied the par-5 10th. Reavie notched back-to-back birdies from the 12th at Fox Den Country Club to grab a piece of the lead at 12-under.
Reavie made it three straight as he birdied the par-4 13th. After that birdie, play was halted for two hours, 17 minutes due to inclement weather.
When play resumed, Reavie parred the final four holes to close a bogey-free round at 13-under.
'I've learned to be patient out here,' admitted Reavie. 'Last year, I would get upset if I wasn't 5-under through 15. This year I've realized that good rounds will come to you.'
McCarthy, who missed the cut in his first two starts this year, was steady over the opening nine holes with two birdies and seven pars.
The delay hit when he was playing the 10th, but he managed a par on that hole anyway. Disaster struck at the 11th where he walked off with a double-bogey.
McCarthy, a 24-year-old rookie, got one stroke back with a birdie on the par-4 12th. He birdied No. 16 to get back within one of the lead before closing with two pars.
'I played solid today except for one bad swing on No. 11,' McCarthy stated. 'I hit the tee shot into some guy's garden.'
Scott Gardiner and Neal Lancaster both shot 68, while Todd Demsey and Kevin Gessino-Kraft carded 69s in round three. They are tied for fifth at 9-under-par 207. Brian Quackenbush, Camilo Benedetti, Esteban Toledo and Brenden Pappas are one stroke further back at minus-8.