Tim O'Neal and Todd Fischer are tied for fourth at 10-under with Deane Pappas, Jim Benepe and Willie Wood another shot back.
Maginnes had a one shot-edge over Tataurangi after the second round and got into red figures for the first time with a six-foot birdie putt at the fourth. He followed up with another birdie two holes later after he drained a 30-foot putt.
Maginnes jumped ahead of the field at the start of his second nine. He hit a 7-iron off the tee at the 207-yard 11th and played it 40 feet left. Maginnes rolled home that long putt and made an eight-footer for birdie at the next hole.
He had an opportunity to go lower when he reached the green in two at the par-5 13th but he could only manage a two-putt birdie. Maginnes had a 12-foot birdie putt at the last hole to build on his lead but missed that and walked off the green in good shape to earn his third win on the Buy.com Tour.
'I would like to have that last putt over,' said Maginnes. 'I would like to be at 15-under but I like my position.'
Maginnes owns two victories on this circuit, the 1998 Dakota Dunes Open and the 1995 San Jose Open.
'It's been a long time and the memory is not quite as good as it used to be,' Maginnes said. 'I was just a kid back then.'
Imada had the shot of the day when he aced the par-3 3rd hole with a 5-iron from 197 yards. He parred the next seven holes before he got to 11-under at the 11th hole.
'It kind of gave me a little too much energy,' said Imada, who carded a 4-under 67 on Saturday. 'I was trying to calm myself down on the next four or five holes where I should have been making birdies. I don't get to have a hole-in-one too many times, so I was a little bit excited.'
Tataurangi came out on fire with four birdies in his first four holes. Two birdies were the result of great wedge play with both putts inside of four feet. The other two came in the form of 15-foot putts.
Tataurangi was one behind Maginnes but ran into trouble at No. 16. He hit a 5-iron into a cactus plant and never recovered, taking a double-bogey on the hole. He finished the round with a 3-under 68.
Paul Claxton is alone in ninth at 6-under 207 and six other golfers, including last week's winner of the Buy.Com Charity Pro-Am, Jonathan Byrd, are tied for 10th.
Full-field scores from the Buy.Com Carolina Classic