Nkhasi, who is based in nearby Soweto, broke clear of Kenyan opponent Edwin Koech in the latter stages of the 10km race to complete the event in 29:48.
Koech held on to take second place in 30:07, and Sibusiso Nzima, who did much of the front running in the early stages, was the first SA athlete home in third (30:10).
Pre-race favourites Elroy Gelant and Stephen Mokoka struggled in the hot conditions, finishing sixth and seventh respectively.
In the women’s race, Lebogang Phalula delivered a superb performance to secure victory in 35:33, just six days after clocking 2:38:00 on her marathon debut in Cape Town.
Zimbabwean athlete Rutendo Nyahora took second position in 35:59 and Glenrose Xaba was third, a further eight seconds off the pace.
Diana-Lebo Phalula, who finished fourth, collapsed after crossing the line and was convulsing while being stretchered away from the finish area, but it was later confirmed that she was recovering well in the medical tent.