EAST LONDON, February 14, 2014 (AFP) - The 1.78-metre rookie carded an eagle and eight birdies and dropped no shots in his 10-under par second round over the 6,064-metre (6,632-yard) shortest European Tour course.
Hahn, who opened with a 65 at the East London Golf Club in the Indian Ocean town, leads by two strokes from first-round pacesetter Ricardo Santos of Portugal.
A 24-year-old graduate of Kent State University in the American mid-west, Hahn is enjoying his first European Tour season after qualifying last year.
"I have been playing pretty well," he said. "Travelling to Africa, Asia and the Middle East in search of prize money and ranking points is a wonderful experience."
Santos returned a five-birdie 66 during a second round delayed 95 minutes by torrential morning rain and has not dropped a shot in the European Tour-Sunshine Tour co-sanctioned event.
Oliver Fisher from England is a further shot behind in third place after a 63 -- the joint second best round of the day with four birdies in each half.
Compatriot David Horsey is alone in fourth spot on 130, firing a second-round 64 in a tournament never won by a non-South African.
Shaun Norris and Retief Goosen were the first winners, and Major champions Charl Schwartzel and Louis Oosthuizen (twice) and Darren Fichardt succeeded when the Africa Open joined the European circuit.
Defending champion Fichardt is the only former winner competing this year and a second-round 67 left him seven strokes behind Hahn.
Leading scores after second 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 Friday (RSA unless noted):
126 - John Hahn (USA) 65-61
128 - Ricardo Santos (POR) 62-66
129 - Oliver Fisher (ENG) 66-63
130 - David Horsey (ENG) 66-64
131 - Thomas Aiken 66-65, Lucas Bjerregaard (DEN) 64-67, Adam Gee (ENG) 66-65, Emiliano Grillo (ARG) 68-63, Fabrizio Zanotti (PAR) 65-66
132 - Jens Dantorp (SWE) 69-63, Garth Mulroy 64-68, Mark Williams 67-65
133 - Darren Fichardt 66-67, James Kamte 69-64, Victor Riu (FRA) 66-67, Simon Wakefield (ENG) 66-67
134 - Ulrich van den Berg 66-68, Gaganjeet Bhullar (IND) 67-67, Jean Hugo 68-66, Jose-Filipe Lima (POR) 67-67, Wade Ormsby (AUS) 70-64, Adrian Otaegui (ESP) 69-65, Ruan de Smidt 68-66, Dawie van der Walt 68-66, Jaco van Zyl 69-65