Todd Rose matched Bellflower's 66 to move into second place at 11-under-par 133. Steve Schneiter, a member this event's host course Willow Creek Country Club, carded a 2-under 70 to take third place at 9-under-par 135.
Bellflower opened on the first tee and quickly moved into red figures with a birdie at the par-5 opening hole. He came back to birdie the par-5 third to move to minus-8.
The 34-year-old dropped in back-to-back birdies from the seventh. Around the turn, he moved to 5 under for his round with a birdie at the par-5 10th.
Bellflower, whose best finish on tour was a tie for second at the 2000 Oregon Classic, made his lone mistake at the par-5 12th. He faltered to a bogey there, but came back with a birdie at the par-4 14th.
Bellflower closed his round with a birdie at the 17th, the fifth and final par-5 at Willow Creek to match his career-best 36-hole score on tour. The lead entering the third round is the first for Bellflower in his career.
'The way the year has been going I've been scraping by and just making cuts,' said Bellflower, who has made just six cuts in 16 starts this year. 'I'm just going to try and enjoy it.'
Rose got off to a rough start as he tripped to a bogey at the par-5 12th, his third. He came right back to birdie the next hole to get back to even par for his round.
The 27-year-old Rose ran off three consecutive birdies from the par-3 15th to move to 8 under overall. Around the turn, Rose dropped in a birdie at the first before back-to-back birdies from the third.
Rose stumbled to his second bogey at the par-3 fifth. He fought back to birdie the seventh to gain second place.
'I'm driving it well and hitting it in the fairways. Even when it's not in the fairway it's in a good spot,' said Rose, a Fresno State graduate. 'Most of the holes out here I've got a wedge in. I don't think I've hit more than an 8-iron into the greens and that helps me because I'm a pretty good wedge player.'
John Merrick fired a 7-under 65 to jump from a share of 66th to a tie for fourth. He is tied at 8-under-par 136 by Chris Sessler, Bubba Watson, Brett Wetterich, Tyler Williamson, Jason Caron and Knoxville Open winner Hunter Haas.
The cut line fell at 3-under-par 141 with exactly 60 players advancing to the weekend. Among those missing out on the final two rounds are Jon Mills, Nick Cassini and Bryce Molder, all at 2-under-par 142, as well as Todd Demsey, Doug LaBelle II, Jeff Quinney and Brad Ott at minus-1.