Joseph Lanza, who shared the lead with Anderson and Eric Jorgensen after two rounds, faltered to a 2-over 72. He is alone in second at minus-2.
Andy Matthews (69) and Matt McQuillan (65) are the final players in red figures at 1-under-par 209. McQuillan's 65 was by two strokes the low round of the day, a day in which just five players carded sub-par rounds in rainy, windy conditions.
Bret Guetz used a 67 to move into a share of fifth at even-par 210. He stands alongside Lee Curry (69).
Anderson got off to a quick start with birdies on one and two. After giving a stroke back on the fifth, Anderson birdied No. 6 at the Highlands Golf Course at Horseshoe Valley Resort.
The 28-year-old faltered to back-to-back bogeys from the seventh to slide to even-par for his round.
Anderson carded two birdies and two bogeys on the back nine to remain at 4 under par.
'It was just kind of one of those rounds -- make a birdie, make a bogey,' stated Anderson, whose lone tour win came last year. 'That bogey on seven took a little wind out of my sails. I was really rolling up to that point. If I didn't have any hiccups this week, I'd be leading this thing by six or seven shots.'
Lanza bogeyed each of the first two holes. He recovered one stroke with a birdie on the fifth. However, he gave that stroke back with a bogey on the eighth. Around the turn, he birdied the 11th and bogeyed 18 to end in second place.
'It wasn't a good ball-striking day,' admitted Lanza. 'But if you have a round like that and still end up two-over on this golf course, you've done some things right. This is where I want to be. I'm obviously not out of the golf tournament and that's all you can ask for.'
Jorgensen struggled to a 5-over 75 and tumbled into a share of seventh at 1-over-par 211. He was joined there by George Bradford and Joe Horowitz.
Ben Bunny, Lucas Bates, Brendan Steele and Michael Walton are one stroke further back at plus-2.