Having turned at the Copperleaf Golf & Country Estate on level par for his round, Northern Ireland's Hoey landed birdies from the 10th to the 16th holes for a seven-under-par 65 that took him to 10-under for the tournament.
The 34-year-old was one of eight players to shoot 65, the low round of the day, including England's Fisher, who eagled the par-five 15th.
Fisher has a 13 under par total of 131. He was a member of Europe's Ryder Cup team in 2010 but has not won on the European Tour since claiming the Irish Open that year.
He is one shot ahead of the Dane Morten Orum Madsen, winner of the 2013 South African Open Championship in November.
Overnight leader Simon Dyson could only manage a 68 and along with the Spaniard Carlos Del Moral was joint third on 11-under.
South Africans Darren Fichardt, Jake Roos and Trevor Fisher Junior were all on 10 under par with Hoey.
Copperleaf Golf & Country Estate is the longest course in European Tour history at 7,964 yards. It has four par-five holes, including the monstrous 685-yard fourth.
(Reporting by Nick Said in Cape Town; editing by Ed Osmond)
