Branden Grace took an early lead during the second round at the BMW SA Open Championship Proudly hosted by the City of Ekurhuleni as the chasing pack were closing in at Glendower Golf Club.
The South African started the day as co-leader with Chase Koepka, younger brother of 2017 US Open Championship winner Brooks, and when he birdied the par four third, he was in front on his own.
Grace, who recorded a trio of eagles in a colourful first round of 65, was one under after eight holes but compatriot Justin Walters sat just one stroke behind following an aggressive start in his opening ten holes.
The 37 year old rolled in gains at the 12th, 13th 15th and 18th to turn in a flawless 32 on his front nine to join overnight co-leader Koepka, who had not started his round, at seven under.
Zimbabwe's Scott Vincent was in equally good form on the second morning, rattling in a birdie at the par five second before three successive gains from the seventh put him two shots behind leader Grace.
South African Richard Sterne registered two birdies and a bogey to sit alongside Vincent at six under, with England's Chris Paisley yet to start on the same score.
Home favourites Charl Schwartzel and Jacques Kruyswijk were among a quintet of players to sit one shot further adrift following eight and six holes respectively, with South Korea's Soomin Lee hitting three birdies in his opening five holes and Spain's Nacho Elvira, who was level par after five, joining former Amateur Championship winner Bradley Neil at five under.