EAST LONDON, February 15, 2014 (AFP) - The 21-year-old Florida-based golfer leads from Englishman Oliver Fisher (66) with South African Thomas Aiken (66), Richard Bland (64) of England and American John Hahn (71) two shots further back.
Grillo is the third leader of the European Tour-Sunshine Tour co-sanctioned event in as many days at the par-71 East London Golf Club after Ricardo Santos of Portugal and Hahn.
Santos slumped to a third-round 73 over the 6,064-metre (6,632-yard) layout and lies eight shots adrift of the leader.
Defending champion Darren Fichardt of South Africa also has considerable catching up to do with a second successive 67 leaving him seven strokes behind Grillo.
The 1.75-metre South American, runner-up to Scot Stephen Gallacher in the Dubai Desert Classic two weeks ago, collected nine birdies and did not drop a shot.
He picked up five on the front nine in the Indian Ocean town, including three on the trot from the sixth, and four more coming back.
Rookie Hahn came down to earth with a bang after his second-round 61, claiming two first-nine birdies only to bogey two holes after the turn.
Major champions Louis Oosthuizen (twice), Charl Schwartzel and Retief Goosen and fellow South Africans Fichardt and Shaun Norris are the previous African Open champions.
Leading scores after third round of European Tour-Sunshine Tour co-sanctioned Africa Open golf tournament at par-71, 6,064-metre (6,632-yard) East London Golf Club Saturday (RSA unless noted):
193 - Emiliano Grillo (ARG) 68-63-62
195 - Oliver Fisher (ENG) 66-63-66
197 - Thomas Aiken 66-65-66, Richard Bland (ENG) 64-69-64, John Hahn (USA) 65-61-71
199 - Ulrich van den Berg 66-68-65, Fabrizio Zanotti (PAR) 65-66-68
200 - Lucas Bjerregaard (DEN) 64-67-69, Jens Dantorp (DEN) 69-63-68, Darren Fichardt 66-67-67, David Horsey (ENG) 66-64-70
201 - Jean Hugo 68-66-67, Ricardo Santos (POR) 62-66-73, Jaco van Zyl 69-65-67