Zander Lombard carded an impressive 65 on Friday to surge into a two-shot lead at the halfway stage of the Nedbank Challenge.
The South African – playing alongside defending champion Lee Westwood and legendary compatriot Ernie Els - managed six birdies and an eagle in a round that included just the one blemish, a bogey five at the first.
Lombard's low score saw him finish the second day of the tournament in Sun City at the top of the leaderboard on 11 under, though his advantage would have been greater had a birdie putt at the last dropped.
Asked if the day ranked as one of his best ever on a golf course, the world number 234 told Sky Sports: "It's definitely up there. Obviously, the nerves are out there for the first few holes, but I settled in quite quickly.
"With Ernie and Lee being lovely gents, we just had an awesome time out there. I really enjoyed today."
Westwood's hopes of defending his title were hit by a round of 73 that included a double-bogey six at the 13th, leaving him on three under. As for Els, an 81 had him languishing down on five over par through 36 holes.
Louis Oosthuizen began the day in front and finished it as compatriot Lombard's closest challenger at the summit, after following up an opening 63 with a level-par 72 to remain nine under.
The 2010 Open champion had been a doubt to play in the tournament due to kidney stones, yet he remains firmly in contention ahead of the weekend.
"Definitely a bit more fatigued today - especially those last six or seven holes," Oosthuizen told Sky Sports. "I hit the tee shot on 14 and felt it a bit on the right side, I think it was a bit more muscular related.
"The stones have passed, so I just need to get some rest and play well tomorrow."
Thomas Detry sat alone in third on seven under; the Belgian having been at one stage in a tie for top spot but successive bogeys on the back nine saw him slip off the pace.
Tommy Fleetwood signed for a second successive 69 to sit tied on six under with Swede Marcus Kinhult in fourth place, a shot clear of Aaron Rai, Jason Scrivener and Joachim B. Hansen.