Sullivan made eight birdies in a flawless round of 64 at 8-under par to take the lead in the first round of the Alfred Dunhill Championship at Leopard Creek Country Club.
The 37-year-old Sullivan, looking to claim his first DP World Tour victory in more than four years, took advantage of cooler conditions before temperatures reached 42 degrees Celsius on the border of Kruger National Park on Thursday afternoon.
Casey Jarvis of South Africa bounced back after bowling three overs in the first two holes to card a 65 and shared second place with Alex Fitzpatrick of England and Marcus Kinhult of Sweden.
Defending champion Louis Oosthuizen was 1 under after scoring a 71 and making three shots on the par-5 18th.
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