Kruger, playing in his home country, had a bogey-free round and O'Hara, from Scotland, combined an eagle, six birdies and a bogey into his 65.
Merrick Bremner, Retief Goosen, David Hewan and Tyrone Mordt -- all South Africans -- are tied for third at 6-under. Four more players are at 5-under.
O'Hara had two birdies in his first three holes but suffered a bogey at the 445-yard, par-4 fourth hole. He had a birdie at No. 7 and then an eagle at the 576-yard, par-5 eighth.
He added back-nine birdies at Nos. 11, 12 and 18.
Kruger, playing the second nine at the Serengeti Golf Club first Thursday, had birdies on 11 and 14 but jumped into contention with three consecutive birdies to make the turn at 5-under. He had birdies at 2 and 7 for his share of the lead.