When play was suspended due to the threat of lightning, South African Trevor Fisher junior was also on seven under after 16 and will complete his final two holes on Friday morning.
"It's a lovely start. It's my lowest round in a good few years, especially on the first day," Dyson said.
"It just puts you in a nice frame of mind, a good stead, and sets it up nicely to have a good weekend."
There are five players a shot back including four-times European Tour winner Darren Fichardt. South Africans have won 10 of the last 13 European Tour events on home soil.
England's Ross Fisher, who has not won since 2010, is also on six under.
Dyson says improvement with the putter was key to his first-round success.
"Putting has been the letdown for the last few weeks, but me and my caddie had a chat about what I'm doing wrong. We spent about an hour and a half on the putting green yesterday and I managed to get a good feel for it," Dyson said.
"I holed a good six-footer for par at the first and then about a 40-footer for birdie at the second and that was it, I was off and running."
Copperleaf Golf & Country Estate is the longest course in European Tour history. It has four par-five holes, including the monstrous 685-yard fourth.
Last year's winner Dawie van der Walt carded a 21-under-par total of 267. He is currently one under after 14 holes.
(Reporting by Nick Said; editing by Robert Woodward;
