Sergio Garcia saw his lead cut to three shots midway through a low-scoring second day of the Nedbank Golf Challenge hosted by Gary Player.
A remarkable 64 on day one of the seventh Rolex Series event of the season handed the Spaniard a four-shot lead overnight and he turned in 33 in round two to get to 11 under.
England's Ross Fisher was putting together a brilliant round and he picked up seven shots in 12 holes to emerge as the nearest challenger at Gary Player Country Club, two shots ahead of countryman Matt Wallace, local favourite Louis Oosthuizen and China's Li Haotong.
Garcia is looking for a first Rolex Series win and a second consecutive victory after his triumph at the Anadalucia Valderrama Masters hosted by his own foundation.
Oosthuizen got within four from ten feet at the first but Garcia holed a 24-footer on the same hole to briefly extend his lead to five.
A nice chip from Oosthuizen cut the gap but the pair were going blow-for-blow, with Garcia getting up and down from over the back of the second before Oosthuizen holed a mid-range putt for a third birdie in four holes on the par-three fourth.
Garcia went right on the fifth and while he played a nice recovery, a three-putt cut his lead to three.
Li needs a win in Sun City to have a chance of winning the Race to Dubai next week and he made a stunning start, making the most of the second, holing a very long putt on the third, hitting a nice approach into the fifth and leaving himself a tap-in on the sixth.
Fisher eagled the second and made a long putt on the fourth before chipping in at the seventh to make a big move.
Li birdied the par-five tenth with Fisher doing the same at the ninth but they were soon four back again as Garcia bounced back from 15 feet at the sixth.
Oosthuizen found huge trouble off the eighth tee after going right for a double-bogey but hit back with a stunning second and an eagle on the par five tenth.
Fisher then made another birdie on the 11th and when he put his tee-shot to six feet on the 12th, the lead was down to two.
That did not last long, however, as Garcia left himself 12 feet at the par-five ninth and moved to 11 under.
Wallace birdied the second and a wonderful approach produced a tap-in birdie at the fifth with another gain coming thanks to a long putt on the seventh. He gave the shot straight back on the next but made a fourth birdie of the day on the tenth.
Wu Ashun and Aaron Rai were six shots off the lead, a shot ahead of Mike Lorenzo-Vera, Lee Westwood and Thomas Detry - who had seven birdies in 12 holes.