South Africa's Branden Grace and American Chase Koepka opened with seven-under-par 65s to lead the BMW SA Open Championship hosted by the City of Ekurhuleni.
Koepka made an eagle, seven birdies and two bogeys to set the target at Glendower Golf Club before Grace made three eagles in his 65 to snatch a share of the lead.
"It was great," the European Tour rookie Koepka said. "I think I played flawless, except for the second shot on the first hole. I hit a poor shot there and saved it with a 12-footer for a bogey. I made eagle on the second hole and kind of kept it going from there.
"Inside 150 yards, I was really good today. I didn't have too many shots from inside 150, but every one that I had, I was hitting them close. The putter was really hot on the front nine, and then I had a bunch of short putts on the back nine which helped a little bit."
Grace replicated Jeff Winther's final round from last year's tournament when he recorded three eagles at the second, eighth and 15th - the last time a player has done this in a single round - in his score of 65.
Koepka and Grace lead by a shot from Scotland's Chris Paisley with former Amateur Championship winner Bradley Neil, South African duo Erik van Rooyen and Richard Sterne and Spain's Nacho Elvira tied on five-under.
South African amateur Kyle McClatchie, joint leader at halfway in last year's Irish Amateur Open at Royal County Down, shot 68 to share eighth with eight others, including fellow amateur Garrick Higgo.
Qualifying School graduate Gavin Moynihan failed to get into the field on his ranking and may now have to wait until next month’s ISPS Handa World Super 6 in Perth or the NBO Oman Open to make his 2018 bow.